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For each service, you can declare build arguments, which are values available to the image only at build time. For example, if you must pass the image a set of credentials in order to access an asset or repository when the image is built, you would pass that value to the image as a build argument.
During a build on Codeship’s Docker platform, there are three ways to pass custom values to your services:
Build arguments are unique in that they are available only at build time. They are not persisted in the image. However, you may assign a build argument to an environment variable during the build process, and that environment variable will be available.
Declaring build arguments in your services file requires updates in two places: the service’s Dockerfile and the
The service’s Dockerfile must include the
ARG instruction, which declares the name of the argument you will pass at build time. You may also declare a default here.
FROM ubuntu:latest ARG build_env # build_env=test would make test the default value RUN script-requiring-build-env.sh "$build_env"
Now that the Dockerfile knows to expect an argument, you can pass the argument to the image via the service configuration in
app: build: dockerfile: Dockerfile args: build_env: staging
app service is built, the value of
staging. If no value was set,
build_env would remain
test. You are not required to declare a default, but you must add an
ARG instruction to the Dockerfile for each build argument you pass in via
You may also declare a build argument before the
FROM instruction, which is a new feature introduced in Docker 17.05. Following the same pattern, you must first declare the argument before consuming it.
ARG BASE_IMAGE_TAG FROM ubuntu:$BASE_IMAGE_TAG
Note: YAML boolean values (true, false, yes, no, on, off) must be enclosed in quotes, so that the parser interprets them as strings.
In a lot of cases, the values needed by the image at build time are secrets – credentials, passwords, and other things that you don’t want to check in to source control in plain text. Because of this, Codeship supports encrypted build arguments. You can either encrypt a build argument individually, or encrypt an entire file containing all of the build arguments you need.
First, create a file in the root directory - in this case, a file named
build_args. You will also need to download the project AES key to root directory (and add it to the
Take care to use
KEY=value syntax and not
Once the AES key is in the root directory, run the
jet encrypt command with an input and an output filename:
jet encrypt build_args build_args.encrypted (Learn more about using Jet)
Pass that file to your service’s build directive.
app: build: dockerfile: Dockerfile encrypted_args_file: build_args.encrypted
If your use case is simple enough, you may want to pass in encrypted values directly instead of requiring Codeship to read them from a file. The following syntax is also supported:
app: build: dockerfile: Dockerfile encrypted_args: 8rD1P1xO1CwB4L99JBqnvoSOX+1wimf9qwHXATf9foasPtU6Sw==
Codeship will decrypt your build arguments and pass them to the image when it is built.
Docker will attempt to reuse layers of your image if there are no changes. Although the values of a build argument are not persisted to the image, they do impact the build cache in a similar way. Refer to Docker’s notes on cache invalidation when using build arguments.
One or more build-args [XXX] were not consumed
If you pass a build argument to an image at build time, but do not have a corresponding
ARG instruction in the Dockerfile, Docker (versions < 1.13) will fail the image build.
As of 1.13, unused build args will not fail the build, but will generate a warning message.
We also have a couple of code examples and sample projects available, that make it easier to get started with Codeship.