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			Markdown
		
	
	
	
	
	
			
		
		
	
	
			593 lines
		
	
	
		
			29 KiB
		
	
	
	
		
			Markdown
		
	
	
	
	
	
# buildx build
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```
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docker buildx build [OPTIONS] PATH | URL | -
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```
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<!---MARKER_GEN_START-->
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Start a build
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### Aliases
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`docker buildx build`, `docker buildx b`
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### Options
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| Name                                                                                                                                                   | Type          | Default   | Description                                                                                         |
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|:-------------------------------------------------------------------------------------------------------------------------------------------------------|:--------------|:----------|:----------------------------------------------------------------------------------------------------|
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| [`--add-host`](https://docs.docker.com/engine/reference/commandline/build/#add-host)                                                                   | `stringSlice` |           | Add a custom host-to-IP mapping (format: `host:ip`)                                                 |
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| [`--allow`](#allow)                                                                                                                                    | `stringSlice` |           | Allow extra privileged entitlement (e.g., `network.host`, `security.insecure`)                      |
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| [`--attest`](#attest)                                                                                                                                  | `stringArray` |           | Attestation parameters (format: `type=sbom,generator=image`)                                        |
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| [`--build-arg`](#build-arg)                                                                                                                            | `stringArray` |           | Set build-time variables                                                                            |
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| [`--build-context`](#build-context)                                                                                                                    | `stringArray` |           | Additional build contexts (e.g., name=path)                                                         |
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| [`--builder`](#builder)                                                                                                                                | `string`      |           | Override the configured builder instance                                                            |
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| [`--cache-from`](#cache-from)                                                                                                                          | `stringArray` |           | External cache sources (e.g., `user/app:cache`, `type=local,src=path/to/dir`)                       |
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| [`--cache-to`](#cache-to)                                                                                                                              | `stringArray` |           | Cache export destinations (e.g., `user/app:cache`, `type=local,dest=path/to/dir`)                   |
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| [`--cgroup-parent`](https://docs.docker.com/engine/reference/commandline/build/#cgroup-parent)                                                         | `string`      |           | Optional parent cgroup for the container                                                            |
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| [`-f`](https://docs.docker.com/engine/reference/commandline/build/#file), [`--file`](https://docs.docker.com/engine/reference/commandline/build/#file) | `string`      |           | Name of the Dockerfile (default: `PATH/Dockerfile`)                                                 |
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| `--iidfile`                                                                                                                                            | `string`      |           | Write the image ID to the file                                                                      |
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| `--invoke`                                                                                                                                             | `string`      |           | Invoke a command after the build [experimental]                                                     |
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| `--label`                                                                                                                                              | `stringArray` |           | Set metadata for an image                                                                           |
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| [`--load`](#load)                                                                                                                                      |               |           | Shorthand for `--output=type=docker`                                                                |
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| [`--metadata-file`](#metadata-file)                                                                                                                    | `string`      |           | Write build result metadata to the file                                                             |
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| `--network`                                                                                                                                            | `string`      | `default` | Set the networking mode for the `RUN` instructions during build                                     |
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| `--no-cache`                                                                                                                                           |               |           | Do not use cache when building the image                                                            |
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| `--no-cache-filter`                                                                                                                                    | `stringArray` |           | Do not cache specified stages                                                                       |
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| [`-o`](#output), [`--output`](#output)                                                                                                                 | `stringArray` |           | Output destination (format: `type=local,dest=path`)                                                 |
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| [`--platform`](#platform)                                                                                                                              | `stringArray` |           | Set target platform for build                                                                       |
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| `--print`                                                                                                                                              | `string`      |           | Print result of information request (e.g., outline, targets) [experimental]                         |
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| [`--progress`](#progress)                                                                                                                              | `string`      | `auto`    | Set type of progress output (`auto`, `plain`, `tty`). Use plain to show container output            |
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| [`--provenance`](#provenance)                                                                                                                          | `string`      |           | Shortand for `--attest=type=provenance`                                                             |
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| `--pull`                                                                                                                                               |               |           | Always attempt to pull all referenced images                                                        |
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| [`--push`](#push)                                                                                                                                      |               |           | Shorthand for `--output=type=registry`                                                              |
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| `-q`, `--quiet`                                                                                                                                        |               |           | Suppress the build output and print image ID on success                                             |
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| [`--sbom`](#sbom)                                                                                                                                      | `string`      |           | Shorthand for `--attest=type=sbom`                                                                  |
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| [`--secret`](#secret)                                                                                                                                  | `stringArray` |           | Secret to expose to the build (format: `id=mysecret[,src=/local/secret]`)                           |
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| [`--shm-size`](#shm-size)                                                                                                                              | `bytes`       | `0`       | Size of `/dev/shm`                                                                                  |
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| [`--ssh`](#ssh)                                                                                                                                        | `stringArray` |           | SSH agent socket or keys to expose to the build (format: `default\|<id>[=<socket>\|<key>[,<key>]]`) |
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| [`-t`](https://docs.docker.com/engine/reference/commandline/build/#tag), [`--tag`](https://docs.docker.com/engine/reference/commandline/build/#tag)    | `stringArray` |           | Name and optionally a tag (format: `name:tag`)                                                      |
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| [`--target`](https://docs.docker.com/engine/reference/commandline/build/#target)                                                                       | `string`      |           | Set the target build stage to build                                                                 |
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| [`--ulimit`](#ulimit)                                                                                                                                  | `ulimit`      |           | Ulimit options                                                                                      |
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<!---MARKER_GEN_END-->
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Flags marked with `[experimental]` need to be explicitly enabled by setting the
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`BUILDX_EXPERIMENTAL=1` environment variable.
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## Description
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The `buildx build` command starts a build using BuildKit. This command is similar
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to the UI of `docker build` command and takes the same flags and arguments.
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For documentation on most of these flags, refer to the [`docker build`
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documentation](https://docs.docker.com/engine/reference/commandline/build/). In
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here we'll document a subset of the new flags.
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## Examples
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### <a name="attest"></a> Create attestations (--attest)
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```
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--attest=type=sbom,...
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--attest=type=provenance,...
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```
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Create [image attestations](https://docs.docker.com/build/attestations/).
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BuildKit currently supports:
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- `sbom` - Software Bill of Materials.
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  Use `--attest=type=sbom` to generate an SBOM for an image at build-time.
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  Alternatively, you can use the [`--sbom` shorthand](#sbom).
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  For more information, see [here](https://docs.docker.com/build/attestations/sbom/).
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- `provenance` - SLSA Provenance
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  Use `--attest=type=provenance` to generate provenance for an image at
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  build-time. Alternatively, you can use the [`--provenance` shorthand](#provenance).
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  For more information, see [here](https://docs.docker.com/build/attestations/slsa-provenance/).
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### <a name="allow"></a> Allow extra privileged entitlement (--allow)
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```
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--allow=ENTITLEMENT
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```
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Allow extra privileged entitlement. List of entitlements:
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- `network.host` - Allows executions with host networking.
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- `security.insecure` - Allows executions without sandbox. See
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  [related Dockerfile extensions](https://docs.docker.com/engine/reference/builder/#run---securitysandbox).
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For entitlements to be enabled, the `buildkitd` daemon also needs to allow them
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with `--allow-insecure-entitlement` (see [`create --buildkitd-flags`](buildx_create.md#buildkitd-flags))
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**Examples**
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```console
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$ docker buildx create --use --name insecure-builder --buildkitd-flags '--allow-insecure-entitlement security.insecure'
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$ docker buildx build --allow security.insecure .
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```
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### <a name="build-arg"></a> Set build-time variables (--build-arg)
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Same as [`docker build` command](https://docs.docker.com/engine/reference/commandline/build/#build-arg).
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There are also useful built-in build args like:
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* `BUILDKIT_CONTEXT_KEEP_GIT_DIR=<bool>` trigger git context to keep the `.git` directory
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* `BUILDKIT_INLINE_BUILDINFO_ATTRS=<bool>` inline build info attributes in image config or not
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* `BUILDKIT_INLINE_CACHE=<bool>` inline cache metadata to image config or not
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* `BUILDKIT_MULTI_PLATFORM=<bool>` opt into deterministic output regardless of multi-platform output or not
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```console
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$ docker buildx build --build-arg BUILDKIT_MULTI_PLATFORM=1 .
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```
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> **Note**
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>
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> More built-in build args can be found in [Dockerfile reference docs](https://docs.docker.com/engine/reference/builder/#buildkit-built-in-build-args).
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### <a name="build-context"></a> Additional build contexts (--build-context)
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```
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--build-context=name=VALUE
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```
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Define additional build context with specified contents. In Dockerfile the context can be accessed when `FROM name` or `--from=name` is used.
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When Dockerfile defines a stage with the same name it is overwritten.
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The value can be a local source directory, [local OCI layout compliant directory](https://github.com/opencontainers/image-spec/blob/main/image-layout.md), container image (with docker-image:// prefix), Git or HTTP URL.
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Replace `alpine:latest` with a pinned one:
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```console
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$ docker buildx build --build-context alpine=docker-image://alpine@sha256:0123456789 .
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```
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Expose a secondary local source directory:
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```console
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$ docker buildx build --build-context project=path/to/project/source .
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# docker buildx build --build-context project=https://github.com/myuser/project.git .
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```
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```dockerfile
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# syntax=docker/dockerfile:1
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FROM alpine
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COPY --from=project myfile /
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```
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#### <a name="source-oci-layout"></a> Source image from OCI layout directory
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Source an image from a local [OCI layout compliant directory](https://github.com/opencontainers/image-spec/blob/main/image-layout.md),
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either by tag, or by digest:
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```console
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$ docker buildx build --build-context foo=oci-layout:///path/to/local/layout:<tag>
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$ docker buildx build --build-context foo=oci-layout:///path/to/local/layout@sha256:<digest>
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```
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```dockerfile
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# syntax=docker/dockerfile:1
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FROM alpine
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RUN apk add git
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COPY --from=foo myfile /
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FROM foo
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```
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The OCI layout directory must be compliant with the [OCI layout specification](https://github.com/opencontainers/image-spec/blob/main/image-layout.md).
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You can reference an image in the layout using either tags, or the exact digest.
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### <a name="builder"></a> Override the configured builder instance (--builder)
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Same as [`buildx --builder`](buildx.md#builder).
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### <a name="cache-from"></a> Use an external cache source for a build (--cache-from)
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```
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--cache-from=[NAME|type=TYPE[,KEY=VALUE]]
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```
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Use an external cache source for a build. Supported types are `registry`,
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`local`, `gha` and `s3`.
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- [`registry` source](https://github.com/moby/buildkit#registry-push-image-and-cache-separately)
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  can import cache from a cache manifest or (special) image configuration on the
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  registry.
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- [`local` source](https://github.com/moby/buildkit#local-directory-1) can
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  import cache from local files previously exported with `--cache-to`.
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- [`gha` source](https://github.com/moby/buildkit#github-actions-cache-experimental)
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  can import cache from a previously exported cache with `--cache-to` in your
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  GitHub repository
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- [`s3` source](https://github.com/moby/buildkit#s3-cache-experimental)
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  can import cache from a previously exported cache with `--cache-to` in your
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  S3 bucket
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If no type is specified, `registry` exporter is used with a specified reference.
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`docker` driver currently only supports importing build cache from the registry.
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```console
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$ docker buildx build --cache-from=user/app:cache .
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$ docker buildx build --cache-from=user/app .
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$ docker buildx build --cache-from=type=registry,ref=user/app .
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$ docker buildx build --cache-from=type=local,src=path/to/cache .
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$ docker buildx build --cache-from=type=gha .
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$ docker buildx build --cache-from=type=s3,region=eu-west-1,bucket=mybucket .
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```
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More info about cache exporters and available attributes: https://github.com/moby/buildkit#export-cache
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### <a name="cache-to"></a> Export build cache to an external cache destination (--cache-to)
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```
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--cache-to=[NAME|type=TYPE[,KEY=VALUE]]
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```
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Export build cache to an external cache destination. Supported types are
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`registry`, `local`, `inline`, `gha` and `s3`.
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- [`registry` type](https://github.com/moby/buildkit#registry-push-image-and-cache-separately) exports build cache to a cache manifest in the registry.
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- [`local` type](https://github.com/moby/buildkit#local-directory-1) exports
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  cache to a local directory on the client.
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- [`inline` type](https://github.com/moby/buildkit#inline-push-image-and-cache-together)
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  writes the cache metadata into the image configuration.
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- [`gha` type](https://github.com/moby/buildkit#github-actions-cache-experimental)
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  exports cache through the [GitHub Actions Cache service API](https://github.com/tonistiigi/go-actions-cache/blob/master/api.md#authentication).
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- [`s3` type](https://github.com/moby/buildkit#s3-cache-experimental) exports
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  cache to a S3 bucket.
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`docker` driver currently only supports exporting inline cache metadata to image
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configuration. Alternatively, `--build-arg BUILDKIT_INLINE_CACHE=1` can be used
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to trigger inline cache exporter.
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Attribute key:
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- `mode` - Specifies how many layers are exported with the cache. `min` on only
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  exports layers already in the final build stage, `max` exports layers for
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  all stages. Metadata is always exported for the whole build.
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```console
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$ docker buildx build --cache-to=user/app:cache .
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$ docker buildx build --cache-to=type=inline .
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$ docker buildx build --cache-to=type=registry,ref=user/app .
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$ docker buildx build --cache-to=type=local,dest=path/to/cache .
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$ docker buildx build --cache-to=type=gha .
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$ docker buildx build --cache-to=type=s3,region=eu-west-1,bucket=mybucket .
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```
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More info about cache exporters and available attributes: https://github.com/moby/buildkit#export-cache
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### <a name="load"></a> Load the single-platform build result to `docker images` (--load)
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Shorthand for [`--output=type=docker`](#docker). Will automatically load the
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single-platform build result to `docker images`.
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### <a name="metadata-file"></a> Write build result metadata to the file (--metadata-file)
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To output build metadata such as the image digest, pass the `--metadata-file` flag.
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The metadata will be written as a JSON object to the specified file. The
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directory of the specified file must already exist and be writable.
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```console
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$ docker buildx build --load --metadata-file metadata.json .
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$ cat metadata.json
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```
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```json
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{
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  "containerimage.buildinfo": {
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    "frontend": "dockerfile.v0",
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    "attrs": {
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      "context": "https://github.com/crazy-max/buildkit-buildsources-test.git#master",
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      "filename": "Dockerfile",
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      "source": "docker/dockerfile:master"
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    },
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    "sources": [
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      {
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        "type": "docker-image",
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        "ref": "docker.io/docker/buildx-bin:0.6.1@sha256:a652ced4a4141977c7daaed0a074dcd9844a78d7d2615465b12f433ae6dd29f0",
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        "pin": "sha256:a652ced4a4141977c7daaed0a074dcd9844a78d7d2615465b12f433ae6dd29f0"
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      },
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      {
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        "type": "docker-image",
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        "ref": "docker.io/library/alpine:3.13",
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        "pin": "sha256:026f721af4cf2843e07bba648e158fb35ecc876d822130633cc49f707f0fc88c"
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      }
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    ]
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  },
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  "containerimage.config.digest": "sha256:2937f66a9722f7f4a2df583de2f8cb97fc9196059a410e7f00072fc918930e66",
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  "containerimage.descriptor": {
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    "annotations": {
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      "config.digest": "sha256:2937f66a9722f7f4a2df583de2f8cb97fc9196059a410e7f00072fc918930e66",
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      "org.opencontainers.image.created": "2022-02-08T21:28:03Z"
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    },
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    "digest": "sha256:19ffeab6f8bc9293ac2c3fdf94ebe28396254c993aea0b5a542cfb02e0883fa3",
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    "mediaType": "application/vnd.oci.image.manifest.v1+json",
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    "size": 506
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  },
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  "containerimage.digest": "sha256:19ffeab6f8bc9293ac2c3fdf94ebe28396254c993aea0b5a542cfb02e0883fa3"
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}
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```
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### <a name="output"></a> Set the export action for the build result (-o, --output)
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```
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-o, --output=[PATH,-,type=TYPE[,KEY=VALUE]
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```
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Sets the export action for the build result. In `docker build` all builds finish
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by creating a container image and exporting it to `docker images`. `buildx` makes
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this step configurable allowing results to be exported directly to the client,
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oci image tarballs, registry etc.
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Buildx with `docker` driver currently only supports local, tarball exporter and
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image exporter. `docker-container` driver supports all the exporters.
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If just the path is specified as a value, `buildx` will use the local exporter
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with this path as the destination. If the value is "-", `buildx` will use `tar`
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exporter and write to `stdout`.
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```console
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$ docker buildx build -o . .
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$ docker buildx build -o outdir .
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$ docker buildx build -o - - > out.tar
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$ docker buildx build -o type=docker .
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$ docker buildx build -o type=docker,dest=- . > myimage.tar
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$ docker buildx build -t tonistiigi/foo -o type=registry
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```
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Supported exported types are:
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#### `local`
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						|
The `local` export type writes all result files to a directory on the client. The
 | 
						|
new files will be owned by the current user. On multi-platform builds, all results
 | 
						|
will be put in subdirectories by their platform.
 | 
						|
 | 
						|
Attribute key:
 | 
						|
 | 
						|
- `dest` - destination directory where files will be written
 | 
						|
 | 
						|
#### `tar`
 | 
						|
 | 
						|
The `tar` export type writes all result files as a single tarball on the client.
 | 
						|
On multi-platform builds all results will be put in subdirectories by their platform.
 | 
						|
 | 
						|
Attribute key:
 | 
						|
 | 
						|
- `dest` - destination path where tarball will be written. “-” writes to stdout.
 | 
						|
 | 
						|
#### `oci`
 | 
						|
 | 
						|
The `oci` export type writes the result image or manifest list as an [OCI image
 | 
						|
layout](https://github.com/opencontainers/image-spec/blob/v1.0.1/image-layout.md)
 | 
						|
tarball on the client.
 | 
						|
 | 
						|
Attribute key:
 | 
						|
 | 
						|
- `dest` - destination path where tarball will be written. “-” writes to stdout.
 | 
						|
 | 
						|
#### `docker`
 | 
						|
 | 
						|
The `docker` export type writes the single-platform result image as a [Docker image
 | 
						|
specification](https://github.com/docker/docker/blob/v20.10.2/image/spec/v1.2.md)
 | 
						|
tarball on the client. Tarballs created by this exporter are also OCI compatible.
 | 
						|
 | 
						|
Currently, multi-platform images cannot be exported with the `docker` export type.
 | 
						|
The most common usecase for multi-platform images is to directly push to a registry
 | 
						|
(see [`registry`](#registry)).
 | 
						|
 | 
						|
Attribute keys:
 | 
						|
 | 
						|
- `dest` - destination path where tarball will be written. If not specified the
 | 
						|
  tar will be loaded automatically to the current docker instance.
 | 
						|
- `context` - name for the docker context where to import the result
 | 
						|
 | 
						|
#### `image`
 | 
						|
 | 
						|
The `image` exporter writes the build result as an image or a manifest list. When
 | 
						|
using `docker` driver the image will appear in `docker images`. Optionally, image
 | 
						|
can be automatically pushed to a registry by specifying attributes.
 | 
						|
 | 
						|
Attribute keys:
 | 
						|
 | 
						|
- `name` - name (references) for the new image.
 | 
						|
- `push` - boolean to automatically push the image.
 | 
						|
 | 
						|
#### `registry`
 | 
						|
 | 
						|
The `registry` exporter is a shortcut for `type=image,push=true`.
 | 
						|
 | 
						|
### <a name="platform"></a> Set the target platforms for the build (--platform)
 | 
						|
 | 
						|
```
 | 
						|
--platform=value[,value]
 | 
						|
```
 | 
						|
 | 
						|
Set the target platform for the build. All `FROM` commands inside the Dockerfile
 | 
						|
without their own `--platform` flag will pull base images for this platform and
 | 
						|
this value will also be the platform of the resulting image. The default value
 | 
						|
will be the current platform of the buildkit daemon.
 | 
						|
 | 
						|
When using `docker-container` driver with `buildx`, this flag can accept multiple
 | 
						|
values as an input separated by a comma. With multiple values the result will be
 | 
						|
built for all of the specified platforms and joined together into a single manifest
 | 
						|
list.
 | 
						|
 | 
						|
If the `Dockerfile` needs to invoke the `RUN` command, the builder needs runtime
 | 
						|
support for the specified platform. In a clean setup, you can only execute `RUN`
 | 
						|
commands for your system architecture.
 | 
						|
If your kernel supports [`binfmt_misc`](https://en.wikipedia.org/wiki/Binfmt_misc)
 | 
						|
launchers for secondary architectures, buildx will pick them up automatically.
 | 
						|
Docker desktop releases come with `binfmt_misc` automatically configured for `arm64`
 | 
						|
and `arm` architectures. You can see what runtime platforms your current builder
 | 
						|
instance supports by running `docker buildx inspect --bootstrap`.
 | 
						|
 | 
						|
Inside a `Dockerfile`, you can access the current platform value through
 | 
						|
`TARGETPLATFORM` build argument. Please refer to the [`docker build`
 | 
						|
documentation](https://docs.docker.com/engine/reference/builder/#automatic-platform-args-in-the-global-scope)
 | 
						|
for the full description of automatic platform argument variants .
 | 
						|
 | 
						|
The formatting for the platform specifier is defined in the [containerd source
 | 
						|
code](https://github.com/containerd/containerd/blob/v1.4.3/platforms/platforms.go#L63).
 | 
						|
 | 
						|
```console
 | 
						|
$ docker buildx build --platform=linux/arm64 .
 | 
						|
$ docker buildx build --platform=linux/amd64,linux/arm64,linux/arm/v7 .
 | 
						|
$ docker buildx build --platform=darwin .
 | 
						|
```
 | 
						|
 | 
						|
### <a name="progress"></a> Set type of progress output (--progress)
 | 
						|
 | 
						|
```
 | 
						|
--progress=VALUE
 | 
						|
```
 | 
						|
 | 
						|
Set type of progress output (auto, plain, tty). Use plain to show container
 | 
						|
output (default "auto").
 | 
						|
 | 
						|
> **Note**
 | 
						|
>
 | 
						|
> You can also use the `BUILDKIT_PROGRESS` environment variable to set its value.
 | 
						|
 | 
						|
The following example uses `plain` output during the build:
 | 
						|
 | 
						|
```console
 | 
						|
$ docker buildx build --load --progress=plain .
 | 
						|
 | 
						|
#1 [internal] load build definition from Dockerfile
 | 
						|
#1 transferring dockerfile: 227B 0.0s done
 | 
						|
#1 DONE 0.1s
 | 
						|
 | 
						|
#2 [internal] load .dockerignore
 | 
						|
#2 transferring context: 129B 0.0s done
 | 
						|
#2 DONE 0.0s
 | 
						|
...
 | 
						|
```
 | 
						|
 | 
						|
> **Note**
 | 
						|
>
 | 
						|
> Check also our [Color output controls guide](https://github.com/docker/buildx/blob/master/docs/guides/color-output.md)
 | 
						|
> for modifying the colors that are used to output information to the terminal.
 | 
						|
 | 
						|
### <a name="provenance"></a> Create provenance attestations (--provenance)
 | 
						|
 | 
						|
Shorthand for [`--attest=type=provenance`](#attest). Enables provenance
 | 
						|
attestations for the build result.
 | 
						|
 | 
						|
### <a name="push"></a> Push the build result to a registry (--push)
 | 
						|
 | 
						|
Shorthand for [`--output=type=registry`](#registry). Will automatically push the
 | 
						|
build result to registry.
 | 
						|
 | 
						|
### <a name="sbom"></a> Create SBOM attestations (--sbom)
 | 
						|
 | 
						|
Shorthand for [`--attest=type=sbom`](#attest). Enables SBOM attestations for
 | 
						|
the build result.
 | 
						|
 | 
						|
### <a name="secret"></a> Secret to expose to the build (--secret)
 | 
						|
 | 
						|
```
 | 
						|
--secret=[type=TYPE[,KEY=VALUE]
 | 
						|
```
 | 
						|
 | 
						|
Exposes secret to the build. The secret can be used by the build using
 | 
						|
[`RUN --mount=type=secret` mount](https://docs.docker.com/engine/reference/builder/#run---mounttypesecret).
 | 
						|
 | 
						|
If `type` is unset it will be detected. Supported types are:
 | 
						|
 | 
						|
#### `file`
 | 
						|
 | 
						|
Attribute keys:
 | 
						|
 | 
						|
- `id` - ID of the secret. Defaults to basename of the `src` path.
 | 
						|
- `src`, `source` - Secret filename. `id` used if unset.
 | 
						|
 | 
						|
```dockerfile
 | 
						|
# syntax=docker/dockerfile:1
 | 
						|
FROM python:3
 | 
						|
RUN pip install awscli
 | 
						|
RUN --mount=type=secret,id=aws,target=/root/.aws/credentials \
 | 
						|
  aws s3 cp s3://... ...
 | 
						|
```
 | 
						|
 | 
						|
```console
 | 
						|
$ docker buildx build --secret id=aws,src=$HOME/.aws/credentials .
 | 
						|
```
 | 
						|
 | 
						|
#### `env`
 | 
						|
 | 
						|
Attribute keys:
 | 
						|
 | 
						|
- `id` - ID of the secret. Defaults to `env` name.
 | 
						|
- `env` - Secret environment variable. `id` used if unset, otherwise will look for `src`, `source` if `id` unset.
 | 
						|
 | 
						|
```dockerfile
 | 
						|
# syntax=docker/dockerfile:1
 | 
						|
FROM node:alpine
 | 
						|
RUN --mount=type=bind,target=. \
 | 
						|
  --mount=type=secret,id=SECRET_TOKEN \
 | 
						|
  SECRET_TOKEN=$(cat /run/secrets/SECRET_TOKEN) yarn run test
 | 
						|
```
 | 
						|
 | 
						|
```console
 | 
						|
$ SECRET_TOKEN=token docker buildx build --secret id=SECRET_TOKEN .
 | 
						|
```
 | 
						|
 | 
						|
### <a name="shm-size"></a> Size of /dev/shm (--shm-size)
 | 
						|
 | 
						|
The format is `<number><unit>`. `number` must be greater than `0`. Unit is
 | 
						|
optional and can be `b` (bytes), `k` (kilobytes), `m` (megabytes), or `g`
 | 
						|
(gigabytes). If you omit the unit, the system uses bytes.
 | 
						|
 | 
						|
### <a name="ssh"></a> SSH agent socket or keys to expose to the build (--ssh)
 | 
						|
 | 
						|
```
 | 
						|
--ssh=default|<id>[=<socket>|<key>[,<key>]]
 | 
						|
```
 | 
						|
 | 
						|
This can be useful when some commands in your Dockerfile need specific SSH
 | 
						|
authentication (e.g., cloning a private repository).
 | 
						|
 | 
						|
`--ssh` exposes SSH agent socket or keys to the build and can be used with the
 | 
						|
[`RUN --mount=type=ssh` mount](https://docs.docker.com/engine/reference/builder/#run---mounttypessh).
 | 
						|
 | 
						|
Example to access Gitlab using an SSH agent socket:
 | 
						|
 | 
						|
```dockerfile
 | 
						|
# syntax=docker/dockerfile:1
 | 
						|
FROM alpine
 | 
						|
RUN apk add --no-cache openssh-client
 | 
						|
RUN mkdir -p -m 0700 ~/.ssh && ssh-keyscan gitlab.com >> ~/.ssh/known_hosts
 | 
						|
RUN --mount=type=ssh ssh -q -T git@gitlab.com 2>&1 | tee /hello
 | 
						|
# "Welcome to GitLab, @GITLAB_USERNAME_ASSOCIATED_WITH_SSHKEY" should be printed here
 | 
						|
# with the type of build progress is defined as `plain`.
 | 
						|
```
 | 
						|
 | 
						|
```console
 | 
						|
$ eval $(ssh-agent)
 | 
						|
$ ssh-add ~/.ssh/id_rsa
 | 
						|
(Input your passphrase here)
 | 
						|
$ docker buildx build --ssh default=$SSH_AUTH_SOCK .
 | 
						|
```
 | 
						|
 | 
						|
### <a name="ulimit"></a> Set ulimits (--ulimit)
 | 
						|
 | 
						|
`--ulimit` is specified with a soft and hard limit as such:
 | 
						|
`<type>=<soft limit>[:<hard limit>]`, for example:
 | 
						|
 | 
						|
```console
 | 
						|
$ docker buildx build --ulimit nofile=1024:1024 .
 | 
						|
```
 | 
						|
 | 
						|
> **Note**
 | 
						|
>
 | 
						|
> If you do not provide a `hard limit`, the `soft limit` is used
 | 
						|
> for both values. If no `ulimits` are set, they are inherited from
 | 
						|
> the default `ulimits` set on the daemon.
 |