Build secrets
A build secret is any piece of sensitive information, such as a password or API token, consumed as part of your application's build process.
Build arguments and environment variables are inappropriate for passing secrets to your build, because they persist in the final image. Instead, you should use secret mounts or SSH mounts, which expose secrets to your builds securely.
Secret mounts
Secret mounts expose secrets to the build containers as files. You
mount the
secrets to the RUN
instructions that
need to access them, similar to how you would define a bind mount or cache
mount.
RUN --mount=type=secret,id=mytoken \
TOKEN=$(cat /run/secrets/mytoken) ...
To pass a secret to a build, use the
docker build --secret
flag, or the
equivalent options for
Bake.
$ 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 a
file or an
environment variable.
When you use the CLI or Bake, the type can be detected automatically. You can
also 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
parameter
to bind the secret to a file with the same name as the variable.
In the following example, the value of the API_TOKEN
variable
is mounted to /run/secrets/API_TOKEN
in the build container.
$ docker build --secret id=API_TOKEN .
Target
By default, secrets are mounted to /run/secrets/<id>
. You can customize the
mount point in the build container using the target
option in the Dockerfile.
The following example mounts the secret to a /root/.aws/credentials
file in
the build container.
$ docker build --secret id=aws,src=/root/.aws/credentials .
RUN --mount=type=secret,id=aws,target=/root/.aws/credentials \
aws s3 cp ...
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 Git repositories is a common use case for SSH mounts.
The following example clones a private GitHub repository using a Dockerfile SSH mount.
# syntax=docker/dockerfile:1
FROM alpine
ADD git@github.com:me/myprivaterepo.git /src/
To pass an SSH socket the build, you use the
docker build --ssh
flag, or equivalent
options for
Bake.
$ docker buildx build --ssh default .
Git authentication for remote contexts
BuildKit supports two pre-defined build secrets, GIT_AUTH_TOKEN
and
GIT_AUTH_HEADER
. Use them to specify HTTP authentication parameters when
building 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 at
https://gitlab.com/example/todo-app.git
, and you want to run a build using
that repository as the build context. An unauthenticated docker build
command
fails 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_TOKEN
environment variable to contain a valid GitLab access token, and pass it as a
secret to the build:
$ GIT_AUTH_TOKEN=$(cat gitlab-token.txt) docker build \
--secret id=GIT_AUTH_TOKEN \
https://gitlab.com/example/todo-app.git
The GIT_AUTH_TOKEN
also works with ADD
to fetch private Git repositories as
part of your build:
FROM alpine
ADD https://gitlab.com/example/todo-app.git /src
HTTP 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 set
the 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.git
BuildKit 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-host
basis, which lets you use different authentication parameters for different
hostnames. To specify a hostname, append the hostname as a suffix to the secret
ID:
$ 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