Earthly 0.8
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Secrets

Secrets are sensitive data that should not be stored in the Earthfile. For example, a password or an API key. Secrets are similar to build arguments, but they are not stored in the Earthfile and are not cached.
Access to secrets is declared explicitly in the commands that need them.

Passing secrets to RUN commands

Here's an example Earthfile that accesses a secret stored under passwd and exposes it under the environment variable mypassword:
FROM alpine:latest
hush:
RUN --secret mypassword=passwd echo "my password is $mypassword"
If the environment variable name is identical to the secret ID. For example to accesses a secret stored under passwd and exposes it under the environment variable passwd you can use the shorthand :
FROM alpine:latest
hush:
RUN --secret passwd echo "my password is $passwd"
It's also possible to temporarily mount a secret as a file:
RUN --mount type=secret,target=/root/mypassword,id=passwd echo "my password is $(cat /root/mypassword)"
The file will not be saved to the image snapshot.

Setting secret values

The value for passwd in examples above must then be supplied when earthly is invoked.
This is possible in a few ways:
  1. 1.
    Directly, on the command line:
    earthly --secret passwd=itsasecret +hush
  2. 2.
    Via an environment variable:
    export passwd=itsasecret
    earthly --secret passwd +hush
    If the value of the secret is omitted on the command line Earthly will lookup the environment variable with that name.
  3. 3.
    Via the environment variable EARTHLY_SECRETS
    export EARTHLY_SECRETS="passwd=itsasecret"
    earthly +hush
    Multiple secrets can be specified by separating them with a comma.
  4. 4.
    Via the .secret file.
    Create a .secret file in the same directory where you plan to run earthly from. Its contents should be:
    passwd=itsasecret
    Then simply run earthly:
    earthly +hello
  5. 5.
    Via cloud-based secrets. This option helps share secrets within a wider team. To read more about this see the cloud-based secrets guide.
Regardless of the approach chosen from above, once earthly is invoked, in our example, it will output:
+hush | --> RUN echo "my password is $mypassword"
+hush | my password is itsasecret

How Arguments and Secrets affect caching

Commands in earthly must be re-evaluated when the command itself changes (e.g. echo "hello $name" is changed to echo "greetings $name"), or when one of its inputs has changed (e.g. --name=world is changed to --name=banana). Earthly creates a hash based on both the contents of the command and the contents of all defined arguments of the target build context.
However, in the case of secrets, the contents of the secret is not included in the hash; therefore, if the contents of a secret changes, Earthly is unable to detect such a change, and thus the command will not be re-evaluated.

Storage of local secrets

Earthly stores the contents of command-line-supplied secrets in memory on the localhost. When a RUN command that requires a secret is evaluated by BuildKit, the BuildKit daemon will request the secret from the earthly command-line process and will temporarily mount the secret inside the runc container that is evaluating the RUN command. Once the command finishes the secret is unmounted. It will not persist as an environment variable within the saved container snapshot. Secrets will be kept in-memory until the earthly command exits.
Earthly also supports cloud-based shared secrets which can be stored in the cloud. Secrets are never stored in the cloud unless a user creates an earthly account and explicitly calls the earthly secrets set ... command to transmit the secret to the earthly cloud-based secrets server.
The benefit of storing secrets in the cloud is that they can be shared in CI and across the team, which helps to reproduce CI builds that much more easily.
For more information about cloud-based secrets, check out our cloud-based secrets management guide.