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A build secret is any piece of sensitive information, such as a password or APItoken, consumed as part of your application's build process.
Build arguments and environment variables are inappropriate for passing secretsto your build, because they persist in the final image. Instead, you should usesecret mounts or SSH mounts, which expose secrets to your builds securely.
Secret mounts expose secrets to the build containers, as files or environmentvariables. You can use secret mounts to pass sensitive information to yourbuilds, such as API tokens, passwords, or SSH keys. Youmount the secrets tothe RUN instructions thatneed to access them, similar to how you would define a bind mount or cachemount.
Passing secrets
To pass a secret to a build, use thedocker build --secretflag, or theequivalent options forBake.
$ docker build --secret id=mytoken,src=$HOME/.aws/credentials .variable "HOME" { default = null}target "default" { secret = [ "id=mytoken,src=${HOME}/.aws/credentials" ]}Sources
The source of a secret can be either afile or anenvironment variable.When you use the CLI or Bake, the type can be detected automatically. You canalso specify it explicitly with type=file or type=env.
The following example mounts the environment variable KUBECONFIG to secret ID kube,as a file in the build container at /run/secrets/kube.
$ docker build --secret id=kube,env=KUBECONFIG .When you use secrets from environment variables, you can omit the env parameterto bind the secret to a file with the same name as the variable.In the following example, the value of the API_TOKEN variableis mounted to /run/secrets/API_TOKEN in the build container.
$ docker build --secret id=API_TOKEN .Target
By default, secrets are mounted as files located at /run/secrets/<id>. Youcan customize how the secrets get mounted in the build container using thetarget and env options for the RUN --mount flag in the Dockerfile.
The following example takes secret id aws and mounts it to /run/secrets/awsin the build container.
RUN --mount=type=secret,id=aws \ AWS_SHARED_CREDENTIALS_FILE=/run/secrets/aws \ aws s3 cp ...To mount a secret as a file with a different name, use the target option inthe --mount flag.
RUN --mount=type=secret,id=aws,target=/root/.aws/credentials \ aws s3 cp ...To mount a secret as an environment variable instead of a file, use theenv option in the --mount flag.
RUN --mount=type=secret,id=aws-key-id,env=AWS_ACCESS_KEY_ID \ --mount=type=secret,id=aws-secret-key,env=AWS_SECRET_ACCESS_KEY \ --mount=type=secret,id=aws-session-token,env=AWS_SESSION_TOKEN \ aws s3 cp ...It's possible to use the target and env options together to mount a secretas both a file and an environment variable.
SSH mounts
If the credential you want to use in your build is an SSH agent socket or key,you can use the SSH mount instead of a secret mount. Cloning private Gitrepositories is a common use case for SSH mounts.
The following example clones a private GitHub repository using aDockerfileSSH mount.
# syntax=docker/dockerfile:1FROM alpineADD git@github.com:me/myprivaterepo.git /src/To pass an SSH socket the build, you use thedocker build --sshflag, or equivalentoptions forBake.
$ docker buildx build --ssh default .Git authentication for remote contexts
BuildKit supports two pre-defined build secrets, GIT_AUTH_TOKEN andGIT_AUTH_HEADER. Use them to specify HTTP authentication parameters whenbuilding with remote, private Git repositories, including:
- Building with a private Git repository as build context
- Fetching private Git repositories in a build with
ADD
For example, say you have a private GitLab project athttps://gitlab.com/example/todo-app.git, and you want to run a build usingthat repository as the build context. An unauthenticated docker build commandfails because the builder isn't authorized to pull the repository:
$ docker build https://gitlab.com/example/todo-app.git[+] Building 0.4s (1/1) FINISHED => ERROR [internal] load git source https://gitlab.com/example/todo-app.git------ > [internal] load git source https://gitlab.com/example/todo-app.git:0.313 fatal: could not read Username for 'https://gitlab.com': terminal prompts disabled------To authenticate the builder to the Git server, set the GIT_AUTH_TOKENenvironment variable to contain a valid GitLab access token, and pass it as asecret to the build:
$ GIT_AUTH_TOKEN=$(cat gitlab-token.txt) docker build \ --secret id=GIT_AUTH_TOKEN \ https://gitlab.com/example/todo-app.gitThe GIT_AUTH_TOKEN also works with ADD to fetch private Git repositories aspart of your build:
FROM alpineADD https://gitlab.com/example/todo-app.git /srcHTTP authentication scheme
By default, Git authentication over HTTP uses the Bearer authentication scheme:
Authorization: Bearer <GIT_AUTH_TOKEN>If you need to use a Basic scheme, with a username and password, you can setthe GIT_AUTH_HEADER build secret:
$ export GIT_AUTH_TOKEN=$(cat gitlab-token.txt)$ export GIT_AUTH_HEADER=basic$ docker build \ --secret id=GIT_AUTH_TOKEN \ --secret id=GIT_AUTH_HEADER \ https://gitlab.com/example/todo-app.gitBuildKit currently only supports the Bearer and Basic schemes.
Multiple hosts
You can set the GIT_AUTH_TOKEN and GIT_AUTH_HEADER secrets on a per-hostbasis, which lets you use different authentication parameters for differenthostnames. To specify a hostname, append the hostname as a suffix to the secretID:
$ export GITLAB_TOKEN=$(cat gitlab-token.txt)$ export GERRIT_TOKEN=$(cat gerrit-username-password.txt)$ export GERRIT_SCHEME=basic$ docker build \ --secret id=GIT_AUTH_TOKEN.gitlab.com,env=GITLAB_TOKEN \ --secret id=GIT_AUTH_TOKEN.gerrit.internal.example,env=GERRIT_TOKEN \ --secret id=GIT_AUTH_HEADER.gerrit.internal.example,env=GERRIT_SCHEME \ https://gitlab.com/example/todo-app.git