docker buildx bake

Description

Bake is a high-level build command. Each specified target runs in parallel as part of the build.

Read High-level build options with Bake guide for introduction to writing bake files.

Options

Examples

Allow extra privileged entitlement (--allow)

--allow=ENTITLEMENT[=VALUE]

Entitlements are designed to provide controlled access to privileged operations. By default, Buildx and BuildKit operates with restricted permissions to protect users and their systems from unintended side effects or security risks. The --allow flag explicitly grants access to additional entitlements, making it clear when a build or bake operation requires elevated privileges.

In addition to BuildKit's network.host and security.insecure entitlements (see docker buildx build --allow), Bake supports file system entitlements that grant granular control over file system access. These are particularly useful when working with builds that need access to files outside the default working directory.

Bake supports the following filesystem entitlements:

• --allow fs=<path|*> - Grant read and write access to files outside of the working directory.
• --allow fs.read=<path|*> - Grant read access to files outside of the working directory.
• --allow fs.write=<path|*> - Grant write access to files outside of the working directory.

The fs entitlements take a path value (relative or absolute) to a directory on the filesystem. Alternatively, you can pass a wildcard (*) to allow Bake to access the entire filesystem.

Bake also supports --allow=buildx.local.delete to grant local outputs permission to delete stale files when mode=delete is set.

Example: fs.read

Given the following Bake configuration, Bake would need to access the parent directory, relative to the Bake file.

target "app" {
  context = "../src"
}

Assuming docker buildx bake app is executed in the same directory as the docker-bake.hcl file, you would need to explicitly allow Bake to read from the ../src directory. In this case, the following invocations all work:

$ docker buildx bake --allow fs.read=* app
$ docker buildx bake --allow fs.read=../src app
$ docker buildx bake --allow fs=* app

Example: fs.write

The following docker-bake.hcl file requires write access to the /tmp directory.

target "app" {
  output = "/tmp"
}

Assuming docker buildx bake app is executed outside of the /tmp directory, you would need to allow the fs.write entitlement, either by specifying the path or using a wildcard:

$ docker buildx bake --allow fs=/tmp app
$ docker buildx bake --allow fs.write=/tmp app
$ docker buildx bake --allow fs.write=* app

Override the configured builder instance (--builder)

Same as buildx --builder.

Invoke a frontend method (--call)

Same as build --call.

Call: check (--check)

Same as build --check.

Configure target execution behavior (--jobs, -j)

--jobs=N
--jobs=[mode,]parallel=N
--jobs=mode

The --jobs flag (shorthand -j) controls target concurrency, output synchronization, and how Bake handles target failures. It accepts an integer as shorthand for parallel=N, or comma-separated mode and parallel options. For example, -j=2 is equivalent to --jobs=parallel=2, and --jobs=defer-error,parallel=2 combines a mode with a concurrency limit. The mode can also be written as mode=defer-error.

The default mode is fail-fast, which stops the build when a target fails and cancels targets that are still running. Outputs already written by successful targets are not removed.

The defer-output mode waits until all participating targets have successfully evaluated their build results before any target begins exporting output. This is useful when multiple targets produce related artifacts and you want to withhold their outputs if a build fails. Exports are not transactional: an export failure can still leave partial output, and completed exports are not rolled back.

For multi-node targets, defer-output applies to the BuildKit solve and export boundary for each target. Any manifest list merge or registry push that Buildx performs after the per-node solves complete is not part of this synchronization barrier.

The defer-error mode allows independent targets to keep running after another target fails. Bake still returns an error after all possible targets complete, but successful targets can finish and write their outputs. Targets that depend on a failed target cannot complete successfully. When --metadata-file is set, Bake writes metadata for successful targets even if another target fails.

$ docker buildx bake --jobs=defer-output # wait for all build results before exporting
$ docker buildx bake --jobs=defer-error  # let independent targets finish before returning an error

The parallel option limits how many Bake targets run at the same time. It requires a non-negative integer. When omitted or set to 0, Bake doesn't apply a target concurrency limit. This controls target scheduling, not BuildKit's internal parallelism for build steps within a target. Specify the mode and limit in the same flag value; repeating --jobs replaces the previous value.

$ docker buildx bake -j=2                          # run at most two targets at the same time
$ docker buildx bake --jobs=parallel=1             # run targets sequentially
$ docker buildx bake --jobs=defer-error,parallel=2 # limit concurrency and let independent targets finish after a failure

With defer-output, every participating target must be able to reach the output boundary before any target completes. A nonzero jobs limit smaller than the number of participating targets is therefore rejected. The same restriction applies when linked targets are present, because their solves may need to be active together. The count includes implicit targets referenced through target: contexts.

Specify a build definition file (-f, --file)

Use the -f / --file option to specify the build definition file to use. The file can be an HCL, JSON or Compose file. If multiple files are specified, all are read and the build configurations are combined.

Alternatively, the environment variable BUILDX_BAKE_FILE can be used to specify the build definition to use. This is mutually exclusive with -f / --file; if both are specified, the environment variable is ignored. Multiple definitions can be specified by separating them with the system's path separator (typically ; on Windows and : elsewhere), but can be changed with BUILDX_BAKE_PATH_SEPARATOR.

By default, local directory build contexts in Bake files are resolved from the current working directory. To opt in to resolving local directory build contexts from the Bake file that defines each path, set BUILDX_BAKE_FILE_RELATIVE_PATHS=1. Compose files use the first Compose file directory as the base, which matches Compose project directory semantics. Use the cwd:// prefix for paths that should remain relative to the current working directory.

You can pass the names of the targets to build, to build only specific target(s). The following example builds the db and webapp-release targets that are defined in the docker-bake.dev.hcl file:

# docker-bake.dev.hcl
group "default" {
  targets = ["db", "webapp-dev"]
}

target "webapp-dev" {
  dockerfile = "Dockerfile.webapp"
  tags = ["docker.io/username/webapp"]
}

target "webapp-release" {
  inherits = ["webapp-dev"]
  platforms = ["linux/amd64", "linux/arm64"]
}

target "db" {
  dockerfile = "Dockerfile.db"
  tags = ["docker.io/username/db"]
}

$ docker buildx bake -f docker-bake.dev.hcl db webapp-release

See the Bake file reference for more details.

List targets and variables (--list)

The --list flag displays all available targets or variables in the Bake configuration, along with a description (if set using the description property in the Bake file).

To list all targets:

$ docker buildx bake --list=targets
TARGET              DESCRIPTION
binaries
default             binaries
update-docs
validate
validate-golangci   Validate .golangci.yml schema (does not run Go linter)

To list variables:

$ docker buildx bake --list=variables
VARIABLE      TYPE      VALUE                DESCRIPTION
REGISTRY      string    docker.io/username   Registry and namespace
IMAGE_NAME    string    my-app               Image name
GO_VERSION              <null>
DEBUG         bool      false                Add debug symbols

Variable types will be shown when set using the type property in the Bake file.

The --list=variables option displays variables defined in the Bake file, including their descriptions and default values.

Example: listing variables with descriptions

variable "GO_VERSION" {
  default     = "1.22"
  description = "Go version used for building the application"
}

$ docker buildx bake --list=variables

NAME          DESCRIPTION                                      DEFAULT
GO_VERSION    Go version used for building the application     1.22

By default, the output of docker buildx bake --list is presented in a table format. Alternatively, you can use a long-form CSV syntax and specify a format attribute to output the list in JSON.

$ docker buildx bake --list=type=targets,format=json

Load images into Docker (--load)

The --load flag is a convenience shorthand for adding an image export of type docker:

--load   ≈   --set=*.output=type=docker

However, its behavior is conditional:

• If the build definition has no output defined, --load adds type=docker.
• If the build definition’s outputs are docker, image, registry, oci, --load will add a type=docker export if one is not already present.
• If the build definition contains local or tar outputs, --load does nothing. It will not override those outputs.

For example, with the following bake file:

target "default" {
  output = ["type=tar,dest=hi.tar"]
}

With --load:

$ docker buildx bake --load --print
...
"output": [
  {
    "dest": "hi.tar"
    "type": "tar",
   }
]

The tar output remains unchanged.

Write build results metadata to a file (--metadata-file)

Similar to buildx build --metadata-file but writes a map of results for each target such as:

# docker-bake.hcl
group "default" {
  targets = ["db", "webapp-dev"]
}

target "db" {
  dockerfile = "Dockerfile.db"
  tags = ["docker.io/username/db"]
}

target "webapp-dev" {
  dockerfile = "Dockerfile.webapp"
  tags = ["docker.io/username/webapp"]
}

$ docker buildx bake --load --metadata-file metadata.json .
$ cat metadata.json

{
  "buildx.build.warnings": {},
  "db": {
    "buildx.build.provenance": {},
    "buildx.build.ref": "mybuilder/mybuilder0/0fjb6ubs52xx3vygf6fgdl611",
    "containerimage.config.digest": "sha256:2937f66a9722f7f4a2df583de2f8cb97fc9196059a410e7f00072fc918930e66",
    "containerimage.descriptor": {
      "annotations": {
        "config.digest": "sha256:2937f66a9722f7f4a2df583de2f8cb97fc9196059a410e7f00072fc918930e66",
        "org.opencontainers.image.created": "2022-02-08T21:28:03Z"
      },
      "digest": "sha256:19ffeab6f8bc9293ac2c3fdf94ebe28396254c993aea0b5a542cfb02e0883fa3",
      "mediaType": "application/vnd.oci.image.manifest.v1+json",
      "size": 506
    },
    "containerimage.digest": "sha256:19ffeab6f8bc9293ac2c3fdf94ebe28396254c993aea0b5a542cfb02e0883fa3"
  },
  "webapp-dev": {
    "buildx.build.provenance": {},
    "buildx.build.ref": "mybuilder/mybuilder0/kamngmcgyzebqxwu98b4lfv3n",
    "containerimage.config.digest": "sha256:9651cc2b3c508f697c9c43b67b64c8359c2865c019e680aac1c11f4b875b67e0",
    "containerimage.descriptor": {
      "annotations": {
        "config.digest": "sha256:9651cc2b3c508f697c9c43b67b64c8359c2865c019e680aac1c11f4b875b67e0",
        "org.opencontainers.image.created": "2022-02-08T21:28:15Z"
      },
      "digest": "sha256:6d9ac9237a84afe1516540f40a0fafdc86859b2141954b4d643af7066d598b74",
      "mediaType": "application/vnd.oci.image.manifest.v1+json",
      "size": 506
    },
    "containerimage.digest": "sha256:6d9ac9237a84afe1516540f40a0fafdc86859b2141954b4d643af7066d598b74"
  }
}

Note

Build record provenance (buildx.build.provenance) includes minimal provenance by default. Set the BUILDX_METADATA_PROVENANCE environment variable to customize this behavior:

• min sets minimal provenance (default).
• max sets full provenance.
• disabled, false or 0 does not set any provenance.

Note

Build warnings (buildx.build.warnings) are not included by default. Set the BUILDX_METADATA_WARNINGS environment variable to 1 or true to include them.

Don't use cache when building the image (--no-cache)

Same as build --no-cache. Don't use cache when building the image.

Print the options without building (--print)

Prints the resulting options of the targets desired to be built, in a JSON format, without starting a build.

$ docker buildx bake -f docker-bake.hcl --print db
{
  "group": {
    "default": {
      "targets": [
        "db"
      ]
    }
  },
  "target": {
    "db": {
      "context": "./",
      "dockerfile": "Dockerfile",
      "tags": [
        "docker.io/tiborvass/db"
      ]
    }
  }
}

Set type of progress output (--progress)

Same as build --progress.

Create provenance attestations (--provenance)

Same as build --provenance.

Always attempt to pull a newer version of the image (--pull)

Same as build --pull.

Push images to a registry (--push)

The --push flag follows the same logic as --load:

• If no outputs are defined, it adds a type=image,push=true export.
• For existing image outputs, it sets push=true.
• If outputs are set to local or tar, it does not override them.

Create SBOM attestations (--sbom)

Same as build --sbom.

Override target configurations from command line (--set)

--set targetpattern.key[.subkey]=value

Override target configurations from command line. The pattern matching syntax is defined in https://golang.org/pkg/path/#Match.

$ docker buildx bake --set target.arg.mybuildarg=value
$ docker buildx bake --set target.platform=linux/arm64
$ docker buildx bake --set foo*.arg.mybuildarg=value    # overrides build arg for all targets starting with 'foo'
$ docker buildx bake --set *.platform=linux/arm64       # overrides platforms for all targets
$ docker buildx bake --set foo*.no-cache                # bypass caching only for targets starting with 'foo'
$ docker buildx bake --set target.platform+=linux/arm64 # appends 'linux/arm64' to the platform list
$ docker buildx bake --set target.contexts.bar=../bar   # overrides 'bar' named context
$ docker buildx bake --set target.resource.memory=2g    # overrides memory resource limit
$ docker buildx bake --set target.secret.aws=env=AWS    # overrides source for an existing secret
$ docker buildx bake --set target.tag=                  # clears all tag values

Note

--set is a repeatable flag. For array fields such as tag, repeat --set to provide multiple values or use the += operator to append without replacing. Array literal syntax like --set target.tag=[a,b] is not supported. For array fields, a non-append assignment with an empty value clears values from the Bake definition and earlier --set flags. Subsequent assignments or appends add values to the cleared array.

You can override the following fields:

• annotation
• attest
• arg.<name>
• cache-from
• cache-to
• call
• context
• contexts.<name>
• dockerfile
• entitlement
• extra-host.<hostname>
• label.<name>
• load
• no-cache
• no-cache-filter
• network
• output
• platform
• policy
• pull
• push
• resource.<field>
• secret
• secret.<id>
• shm-size
• ssh
• tag
• target
• ulimit

You can append using += operator for the following fields:

• annotation¹
• attest¹
• cache-from
• cache-to
• entitlement¹
• no-cache-filter
• output
• platform
• policy
• secret
• ssh
• tag
• ulimit

Note

¹ These fields already append by default.

Override keys use singular names. Existing plural Bake field names and historical --set spellings remain supported as aliases:

Aliases are normalized before overrides are applied, so they can be mixed with canonical keys in repeated --set options. context and contexts are not aliases: context sets the build context, while contexts.<name> sets a named context. secret.<id> also has separate semantics: it changes the source of a secret that is already declared by the target. The plural alias does not support this form; secrets.<id> is invalid.

Inline values for composable attributes

Composable fields such as ssh, secret, output, cache-to, cache-from, attest, and annotation accept a list of object values in a Bake file. When you override these fields with --set, provide each value using the same inline string syntax as the corresponding build flag, not the HCL object form. The override replaces or appends to the list as a whole and does not address individual object fields with a subkey.

Only arg, contexts, extra-host, label, resource, and secret support entry-addressed subkeys. For example, use --set target.arg.MYARG=value to override one build argument. As described above, secret.<id> changes the source of an existing secret rather than an object field.

For example, to set the SSH agent socket or key for a target, use the same id=path form accepted by build --ssh:

$ docker buildx bake --set "*.ssh=default=$HOME/.ssh/id_ed25519"

To expose multiple paths for the same id, separate them with commas in the second part:

$ docker buildx bake --set "*.ssh=default=$HOME/.ssh/id_ed25519,$HOME/.ssh/id_rsa"

Your shell expands $HOME before buildx sees the value. The equivalent Bake file definition uses the homedir HCL function:

target "default" {
  ssh = [{ id = "default", paths = ["${homedir()}/.ssh/id_ed25519", "${homedir()}/.ssh/id_rsa"] }]
}