docker buildx build

Description

The docker buildx build command starts a build using BuildKit.

Options

Examples

Add entries to container hosts file (--add-host)

You can add other hosts into a build container's /etc/hosts file by using one or more --add-host flags. This example adds static addresses for hosts named my-hostname and my_hostname_v6:

$ docker buildx build --add-host my_hostname=8.8.8.8 --add-host my_hostname_v6=2001:4860:4860::8888 .

If you need your build to connect to services running on the host, you can use the special host-gateway value for --add-host. In the following example, build containers resolve host.docker.internal to the host's gateway IP.

$ docker buildx build --add-host host.docker.internal=host-gateway .

You can wrap an IPv6 address in square brackets. = and : are both valid separators. Both formats in the following example are valid:

$ docker buildx build --add-host my-hostname:10.180.0.1 --add-host my-hostname_v6=[2001:4860:4860::8888] .

Create annotations (--annotation)

--annotation="key=value"
--annotation="[type:]key=value"

Add OCI annotations to the image index, manifest, or descriptor. The following example adds the foo=bar annotation to the image manifests:

$ docker buildx build -t TAG --annotation "foo=bar" --push .

You can optionally add a type prefix to specify the level of the annotation. By default, the image manifest is annotated. The following example adds the foo=bar annotation the image index instead of the manifests:

$ docker buildx build -t TAG --annotation "index:foo=bar" --push .

You can specify multiple types, separated by a comma (,) to add the annotation to multiple image components. The following example adds the foo=bar annotation to image index, descriptors, manifests:

$ docker buildx build -t TAG --annotation "index,manifest,manifest-descriptor:foo=bar" --push .

You can also specify a platform qualifier in square brackets ([os/arch]) in the type prefix, to apply the annotation to a subset of manifests with the matching platform. The following example adds the foo=bar annotation only to the manifest with the linux/amd64 platform:

$ docker buildx build -t TAG --annotation "manifest[linux/amd64]:foo=bar" --push .

Wildcards are not supported in the platform qualifier; you can't specify a type prefix like manifest[linux/*] to add annotations only to manifests which has linux as the OS platform.

For more information about annotations, see Annotations.

Create attestations (--attest)

--attest=type=sbom,...
--attest=type=provenance,...

Create image attestations. BuildKit currently supports:

• sbom - Software Bill of Materials.

  Use --attest=type=sbom to generate an SBOM for an image at build-time. Alternatively, you can use the --sbom shorthand.

  For more information, see here.

• provenance - SLSA Provenance

  Use --attest=type=provenance to generate provenance for an image at build-time. Alternatively, you can use the --provenance shorthand.

  By default, a minimal provenance attestation will be created for the build result, which will only be attached for images pushed to registries.

  For more information, see here.

Allow extra privileged entitlement (--allow)

--allow=ENTITLEMENT

Allow extra privileged entitlement. List of entitlements:

• network.host - Allows executions with host networking.
• security.insecure - Allows executions without sandbox. See related Dockerfile extensions.

For entitlements to be enabled, the BuildKit daemon also needs to allow them with --allow-insecure-entitlement (see create --buildkitd-flags).

$ docker buildx create --use --name insecure-builder --buildkitd-flags '--allow-insecure-entitlement security.insecure'
$ docker buildx build --allow security.insecure .

Set build-time variables (--build-arg)

You can use ENV instructions in a Dockerfile to define variable values. These values persist in the built image. Often persistence isn't what you want. Users want to specify variables differently depending on which host they build an image on.

A good example is http_proxy or source versions for pulling intermediate files. The ARG instruction lets Dockerfile authors define values that users can set at build-time using the --build-arg flag:

$ docker buildx build --build-arg HTTP_PROXY=http://10.20.30.2:1234 --build-arg FTP_PROXY=http://40.50.60.5:4567 .

This flag allows you to pass the build-time variables that are accessed like regular environment variables in the RUN instruction of the Dockerfile. These values don't persist in the intermediate or final images like ENV values do. You must add --build-arg for each build argument.

Using this flag doesn't alter the output you see when the build process echoes theARG lines from the Dockerfile.

For detailed information on using ARG and ENV instructions, see the Dockerfile reference.

You can also use the --build-arg flag without a value, in which case the daemon propagates the value from the local environment into the Docker container it's building:

$ export HTTP_PROXY=http://10.20.30.2:1234
$ docker buildx build --build-arg HTTP_PROXY .

This example is similar to how docker run -e works. Refer to the docker run documentation for more information.

There are also useful built-in build arguments, such as:

• BUILDKIT_CONTEXT_KEEP_GIT_DIR=<bool>: trigger git context to keep the .git directory
• BUILDKIT_INLINE_CACHE=<bool>: inline cache metadata to image config or not
• BUILDKIT_MULTI_PLATFORM=<bool>: opt into deterministic output regardless of multi-platform output or not

$ docker buildx build --build-arg BUILDKIT_MULTI_PLATFORM=1 .

Learn more about the built-in build arguments in the Dockerfile reference docs.

Additional build contexts (--build-context)

--build-context=name=VALUE

Define additional build context with specified contents. In Dockerfile the context can be accessed when FROM name or --from=name is used. When Dockerfile defines a stage with the same name it is overwritten.

The value can be a local source directory, local OCI layout compliant directory, container image (with docker-image:// prefix), Git or HTTP URL.

Replace alpine:latest with a pinned one:

$ docker buildx build --build-context alpine=docker-image://alpine@sha256:0123456789 .

Expose a secondary local source directory:

$ docker buildx build --build-context project=path/to/project/source .
# docker buildx build --build-context project=https://github.com/myuser/project.git .

# syntax=docker/dockerfile:1
FROM alpine
COPY --from=project myfile /

Use an OCI layout directory as build context

Source an image from a local OCI layout compliant directory, either by tag, or by digest:

$ docker buildx build --build-context foo=oci-layout:///path/to/local/layout:<tag>
$ docker buildx build --build-context foo=oci-layout:///path/to/local/layout@sha256:<digest>

# syntax=docker/dockerfile:1
FROM alpine
RUN apk add git
COPY --from=foo myfile /

FROM foo

The OCI layout directory must be compliant with the OCI layout specification. You can reference an image in the layout using either tags, or the exact digest.

Override the configured builder instance (--builder)

Same as buildx --builder.

Use an external cache source for a build (--cache-from)

--cache-from=[NAME|type=TYPE[,KEY=VALUE]]

Use an external cache source for a build. Supported types are registry, local, gha and s3.

• registry source can import cache from a cache manifest or (special) image configuration on the registry.
• local source can import cache from local files previously exported with --cache-to.
• gha source can import cache from a previously exported cache with --cache-to in your GitHub repository
• s3 source can import cache from a previously exported cache with --cache-to in your S3 bucket

If no type is specified, registry exporter is used with a specified reference.

docker driver currently only supports importing build cache from the registry.

$ docker buildx build --cache-from=user/app:cache .
$ docker buildx build --cache-from=user/app .
$ docker buildx build --cache-from=type=registry,ref=user/app .
$ docker buildx build --cache-from=type=local,src=path/to/cache .
$ docker buildx build --cache-from=type=gha .
$ docker buildx build --cache-from=type=s3,region=eu-west-1,bucket=mybucket .

More info about cache exporters and available attributes: https://github.com/moby/buildkit#export-cache

Invoke a frontend method (--call)

--call=[build|check|outline|targets]

BuildKit frontends can support alternative modes of executions for builds, using frontend methods. Frontend methods are a way to change or extend the behavior of a build invocation, which lets you, for example, inspect, validate, or generate alternative outputs from a build.

The --call flag for docker buildx build lets you specify the frontend method that you want to execute. If this flag is unspecified, it defaults to executing the build and evaluating build checks.

For Dockerfiles, the available methods are:

Note that other frontends may implement these or other methods. To see the list of available methods for the frontend you're using, use --call=subrequests.describe.

$ docker buildx build -q --call=subrequests.describe .

NAME                 VERSION DESCRIPTION
outline              1.0.0   List all parameters current build target supports
targets              1.0.0   List all targets current build supports
subrequests.describe 1.0.0   List available subrequest types

Descriptions

The --call=targets and --call=outline methods include descriptions for build targets and arguments, if available. Descriptions are generated from comments in the Dockerfile. A comment on the line before a FROM instruction becomes the description of a build target, and a comment before an ARG instruction the description of a build argument. The comment must lead with the name of the stage or argument, for example:

# syntax=docker/dockerfile:1

# GO_VERSION sets the Go version for the build
ARG GO_VERSION=1.22

# base-builder is the base stage for building the project
FROM golang:${GO_VERSION} AS base-builder

When you run docker buildx build --call=outline, the output includes the descriptions, as follows:

$ docker buildx build -q --call=outline .

TARGET:      base-builder
DESCRIPTION: is the base stage for building the project

BUILD ARG    VALUE   DESCRIPTION
GO_VERSION   1.22    sets the Go version for the build

For more examples on how to write Dockerfile docstrings, check out the Dockerfile for Docker docs.

Call: check (--check)

The check method evaluates build checks without executing the build. The --check flag is a convenient shorthand for --call=check. Use the check method to validate the build configuration before starting the build.

$ docker buildx build -q --check https://github.com/docker/docs.git

WARNING: InvalidBaseImagePlatform
Base image wjdp/htmltest:v0.17.0 was pulled with platform "linux/amd64", expected "linux/arm64" for current build
Dockerfile:43
--------------------
  41 |         "#content/desktop/previous-versions/*.md"
  42 |
  43 | >>> FROM wjdp/htmltest:v${HTMLTEST_VERSION} AS test
  44 |     WORKDIR /test
  45 |     COPY --from=build /out ./public
--------------------

Using --check without specifying a target evaluates the entire Dockerfile. If you want to evaluate a specific target, use the --target flag.

Call: outline

The outline method prints the name of the specified target (or the default target, if --target isn't specified), and the build arguments that the target consumes, along with their default values, if set.

The following example shows the default target release and its build arguments:

$ docker buildx build -q --call=outline https://github.com/docker/docs.git

TARGET:      release
DESCRIPTION: is an empty scratch image with only compiled assets

BUILD ARG          VALUE     DESCRIPTION
GO_VERSION         1.22      sets the Go version for the base stage
HUGO_VERSION       0.127.0
HUGO_ENV                     sets the hugo.Environment (production, development, preview)
DOCS_URL                     sets the base URL for the site
PAGEFIND_VERSION   1.1.0

This means that the release target is configurable using these build arguments:

$ docker buildx build \
  --build-arg GO_VERSION=1.22 \
  --build-arg HUGO_VERSION=0.127.0 \
  --build-arg HUGO_ENV=production \
  --build-arg DOCS_URL=https://example.com \
  --build-arg PAGEFIND_VERSION=1.1.0 \
  --target release https://github.com/docker/docs.git

Call: targets

The targets method lists all the build targets in the Dockerfile. These are the stages that you can build using the --target flag. It also indicates the default target, which is the target that will be built when you don't specify a target.

$ docker buildx build -q --call=targets https://github.com/docker/docs.git

TARGET            DESCRIPTION
base              is the base stage with build dependencies
node              installs Node.js dependencies
hugo              downloads and extracts the Hugo binary
build-base        is the base stage for building the site
dev               is for local development with Docker Compose
build             creates production builds with Hugo
lint              lints markdown files
test              validates HTML output and checks for broken links
update-modules    downloads and vendors Hugo modules
vendor            is an empty stage with only vendored Hugo modules
build-upstream    builds an upstream project with a replacement module
validate-upstream validates HTML output for upstream builds
unused-media      checks for unused graphics and other media
pagefind          installs the Pagefind runtime
index             generates a Pagefind index
test-go-redirects checks that the /go/ redirects are valid
release (default) is an empty scratch image with only compiled assets

Export build cache to an external cache destination (--cache-to)

--cache-to=[NAME|type=TYPE[,KEY=VALUE]]

Export build cache to an external cache destination. Supported types are registry, local, inline, gha and s3.

• registry type exports build cache to a cache manifest in the registry.
• local type exports cache to a local directory on the client.
• inline type writes the cache metadata into the image configuration.
• gha type exports cache through the GitHub Actions Cache service API.
• s3 type exports cache to a S3 bucket.

The docker driver only supports cache exports using the inline and local cache backends.

Attribute key:

• mode - Specifies how many layers are exported with the cache. min on only exports layers already in the final build stage, max exports layers for all stages. Metadata is always exported for the whole build.

$ docker buildx build --cache-to=user/app:cache .
$ docker buildx build --cache-to=type=inline .
$ docker buildx build --cache-to=type=registry,ref=user/app .
$ docker buildx build --cache-to=type=local,dest=path/to/cache .
$ docker buildx build --cache-to=type=gha .
$ docker buildx build --cache-to=type=s3,region=eu-west-1,bucket=mybucket .

More info about cache exporters and available attributes: https://github.com/moby/buildkit#export-cache

Use a custom parent cgroup (--cgroup-parent)

When you run docker buildx build with the --cgroup-parent option, the daemon runs the containers used in the build with the corresponding docker run flag.

Specify a Dockerfile (-f, --file)

$ docker buildx build -f <filepath> .

Specifies the filepath of the Dockerfile to use. If unspecified, a file named Dockerfile at the root of the build context is used by default.

To read a Dockerfile from stdin, you can use - as the argument for --file.

$ cat Dockerfile | docker buildx build -f - .

Load the single-platform build result to docker images (--load)

Shorthand for --output=type=docker. Will automatically load the single-platform build result to docker images.

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

To output build metadata such as the image digest, pass the --metadata-file flag. The metadata will be written as a JSON object to the specified file. The directory of the specified file must already exist and be writable.

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

{
  "buildx.build.provenance": {},
  "buildx.build.ref": "mybuilder/mybuilder0/0fjb6ubs52xx3vygf6fgdl611",
  "buildx.build.warnings": {},
  "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"
}

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 doesn't 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.

Set the networking mode for the RUN instructions during build (--network)

Available options for the networking mode are:

• default (default): Run in the default network.
• none: Run with no network access.
• host: Run in the host’s network environment.

Find more details in the Dockerfile reference.

Ignore build cache for specific stages (--no-cache-filter)

The --no-cache-filter lets you specify one or more stages of a multi-stage Dockerfile for which build cache should be ignored. To specify multiple stages, use a comma-separated syntax:

$ docker buildx build --no-cache-filter stage1,stage2,stage3 .

For example, the following Dockerfile contains four stages:

• base
• install
• test
• release

# syntax=docker/dockerfile:1

FROM oven/bun:1 AS base
WORKDIR /app

FROM base AS install
WORKDIR /temp/dev
RUN --mount=type=bind,source=package.json,target=package.json \
    --mount=type=bind,source=bun.lockb,target=bun.lockb \
    bun install --frozen-lockfile

FROM base AS test
COPY --from=install /temp/dev/node_modules node_modules
COPY . .
RUN bun test

FROM base AS release
ENV NODE_ENV=production
COPY --from=install /temp/dev/node_modules node_modules
COPY . .
ENTRYPOINT ["bun", "run", "index.js"]

To ignore the cache for the install stage:

$ docker buildx build --no-cache-filter install .

To ignore the cache the install and release stages:

$ docker buildx build --no-cache-filter install,release .

The arguments for the --no-cache-filter flag must be names of stages.

Set the export action for the build result (-o, --output)

-o, --output=[PATH,-,type=TYPE[,KEY=VALUE]

Sets the export action for the build result. The default output, when using the docker build driver, is a container image exported to the local image store. The --output flag makes this step configurable allows export of results directly to the client's filesystem, an OCI image tarball, a registry, and more.

Buildx with docker driver only supports the local, tarball, and image exporters. The docker-container driver supports all exporters.

If you only specify a filepath as the argument to --output, Buildx uses the local exporter. If the value is -, Buildx uses the tar exporter and writes the output to stdout.

$ docker buildx build -o . .
$ docker buildx build -o outdir .
$ docker buildx build -o - . > out.tar
$ docker buildx build -o type=docker .
$ docker buildx build -o type=docker,dest=- . > myimage.tar
$ docker buildx build -t tonistiigi/foo -o type=registry

You can export multiple outputs by repeating the flag.

Supported exported types are:

• local
• tar
• oci
• docker
• image
• registry

local

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

For more information, see Local and tar exporters.

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.

For more information, see Local and tar exporters.

oci

The oci export type writes the result image or manifest list as an OCI image layout tarball on the client.

Attribute key:

• dest - destination path where tarball will be written. “-” writes to stdout.

For more information, see OCI and Docker exporters.

docker

The docker export type writes the single-platform result image as a Docker image specification tarball on the client. Tarballs created by this exporter are also OCI compatible.

The default image store in Docker Engine doesn't support loading multi-platform images. You can enable the containerd image store, or push multi-platform images is to directly push to a registry, see registry.

Attribute keys:

• dest - destination path where tarball will be written. If not specified, the tar will be loaded automatically to the local image store.
• context - name for the Docker context where to import the result

For more information, see OCI and Docker exporters.

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.

For more information, see Image and registry exporters.

registry

The registry exporter is a shortcut for type=image,push=true.

For more information, see Image and registry exporters.

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 is the platform of the BuildKit daemon where the build runs. The value takes the form of os/arch or os/arch/variant. For example, linux/amd64 or linux/arm/v7. Additionally, the --platform flag also supports a special local value, which tells BuildKit to use the platform of the BuildKit client that invokes the build.

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 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. Refer to the Dockerfile reference for the full description of automatic platform argument variants .

You can find the formatting definition for the platform specifier in the containerd source code.

$ docker buildx build --platform=linux/arm64 .
$ docker buildx build --platform=linux/amd64,linux/arm64,linux/arm/v7 .
$ docker buildx build --platform=darwin .

Set type of progress output (--progress)

--progress=VALUE

Set type of progress output (auto, plain, tty, rawjson). 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:

$ 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 the BUILDKIT_COLORS environment variable for modifying the colors of the terminal output.

The rawjson output marshals the solve status events from BuildKit to JSON lines. This mode is designed to be read by an external program.

Create provenance attestations (--provenance)

Shorthand for --attest=type=provenance, used to configure provenance attestations for the build result. For example, --provenance=mode=max can be used as an abbreviation for --attest=type=provenance,mode=max.

Additionally, --provenance can be used with Boolean values to enable or disable provenance attestations. For example, --provenance=false disables all provenance attestations, while --provenance=true enables all provenance attestations.

By default, a minimal provenance attestation will be created for the build result. Note that the default image store in Docker Engine doesn't support attestations. Provenance attestations only persist for images pushed directly to a registry if you use the default image store. Alternatively, you can switch to using the containerd image store.

For more information about provenance attestations, see here.

Push the build result to a registry (--push)

Shorthand for --output=type=registry. Will automatically push the build result to registry.

Create SBOM attestations (--sbom)

Shorthand for --attest=type=sbom, used to configure SBOM attestations for the build result. For example, --sbom=generator=<user>/<generator-image> can be used as an abbreviation for --attest=type=sbom,generator=<user>/<generator-image>.

Additionally, --sbom can be used with Boolean values to enable or disable SBOM attestations. For example, --sbom=false disables all SBOM attestations.

Note that the default image store in Docker Engine doesn't support attestations. Provenance attestations only persist for images pushed directly to a registry if you use the default image store. Alternatively, you can switch to using the containerd image store.

For more information, see here.

Secret to expose to the build (--secret)

--secret=[type=TYPE[,KEY=VALUE]

Exposes secrets (authentication credentials, tokens) to the build. A secret can be mounted into the build using a RUN --mount=type=secret mount in the Dockerfile. For more information about how to use build secrets, see Build secrets.

Supported types are:

• type=file
• type=env

Buildx attempts to detect the type automatically if unset. If an environment variable with the same key as id is set, then Buildx uses type=env and the variable value becomes the secret. If no such environment variable is set, and type is not set, then Buildx falls back to type=file.

type=file

Source a build secret from a file.

type=file synopsis

$ docker buildx build --secret [type=file,]id=<ID>[,src=<FILEPATH>] .

type=file attributes

type=file usage

In the following example, type=file is automatically detected because no environment variable mathing aws (the ID) is set.

$ docker buildx build --secret id=aws,src=$HOME/.aws/credentials .

# 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://... ...

type=env

Source a build secret from an environment variable.

type=env synopsis

$ docker buildx build --secret [type=env,]id=<ID>[,env=<VARIABLE>] .

type=env attributes

type=env usage

In the following example, type=env is automatically detected because an environment variable matching id is set.

$ SECRET_TOKEN=token docker buildx build --secret id=SECRET_TOKEN .

# syntax=docker/dockerfile:1
FROM node:alpine
RUN --mount=type=bind,target=. \
  --mount=type=secret,id=SECRET_TOKEN,env=SECRET_TOKEN \
  yarn run test

In the following example, the build argument SECRET_TOKEN is set to contain the value of the environment variable API_KEY.

$ API_KEY=token docker buildx build --secret id=SECRET_TOKEN,env=API_KEY .

You can also specify the name of the environment variable with src or source:

$ API_KEY=token docker buildx build --secret type=env,id=SECRET_TOKEN,src=API_KEY .

Note

Specifying the environment variable name with src or source, you are required to set type=env explicitly, or else Buildx assumes that the secret is type=file, and looks for a file with the name of src or source (in this case, a file named API_KEY relative to the location where the docker buildx build command was executed.

Shared memory size for build containers (--shm-size)

Sets the size of the shared memory allocated for build containers when using RUN instructions.

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.

Note

In most cases, it is recommended to let the builder automatically determine the appropriate configurations. Manual adjustments should only be considered when specific performance tuning is required for complex build scenarios.

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.

Example to access Gitlab using an SSH agent socket:

# 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`.

$ eval $(ssh-agent)
$ ssh-add ~/.ssh/id_rsa
(Input your passphrase here)
$ docker buildx build --ssh default=$SSH_AUTH_SOCK .

Tag an image (-t, --tag)

$ docker buildx build -t docker/apache:2.0 .

This examples builds in the same way as the previous example, but it then tags the resulting image. The repository name will be docker/apache and the tag 2.0.

Read more about valid tags.

You can apply multiple tags to an image. For example, you can apply the latest tag to a newly built image and add another tag that references a specific version.

For example, to tag an image both as docker/fedora-jboss:latest and docker/fedora-jboss:v2.1, use the following:

$ docker buildx build -t docker/fedora-jboss:latest -t docker/fedora-jboss:v2.1 .

Specifying target build stage (--target)

When building a Dockerfile with multiple build stages, use the --target option to specify an intermediate build stage by name as a final stage for the resulting image. The builder skips commands after the target stage.

FROM debian AS build-env
# ...

FROM alpine AS production-env
# ...

$ docker buildx build -t mybuildimage --target build-env .

Set ulimits (--ulimit)

--ulimit overrides the default ulimits of build's containers when using RUN instructions and are specified with a soft and hard limit as such: <type>=<soft limit>[:<hard limit>], for example:

$ docker buildx build --ulimit nofile=1024:1024 .

Note

If you don't provide a hard limit, the soft limit is used for both values. If no ulimits are set, they're inherited from the default ulimits set on the daemon.

Note

In most cases, it is recommended to let the builder automatically determine the appropriate configurations. Manual adjustments should only be considered when specific performance tuning is required for complex build scenarios.