hooks.md

Hooks

Sometimes you want to run a command before other commands. Some examples:

• you have a number of ops commands that let a developer run different test suites inside a container, and you want to make sure the container image is built beforehand
• you have some configuration that needs to happen when the software execution environment changes (e.g. going from dev to staging)

In this case, you can use the "hooks feature.

Before hooks

"Before hooks" run before actions. They do not run before builtins like up or exec.

hooks:
  before:
    - bin/build-container.sh
actions:
  test:
    command: docker run --rm test_container

You may have some actions that don't need to run before hooks. For example, an action that removes container images to allow a developer to force a clean build from the latest source, or free up disk space.

In this case, you can configure that action to skip the hooks:

hooks:
  before:
    - bin/build-container.sh
actions:
  test:
    command: docker run --rm test_image
  remove-image:
    command: docker rm test_image
    skip_before_hooks: true

Hooks in ops actions called from ops actions

You may have ops actions that call ops actions. For example, an action that calls terraform apply and another one that calls that one, adding the --auto-approve parameter:

hooks:
  before:
    - ln -sf backend/$environment/backend.tf .
    - ops terraform-init
actions:
  apply:
    command: terraform apply
    load_secrets: true
  apply-auto-approve:
    command: ops apply --auto-approve
    alias: aa
  terraform-init:
    command: terraform init --backend-config=...
    load_secrets: true

These two hooks ensure that terraform can always find the appropriate backend for the current software execution environment (e.g. dev vs staging) environment. However, you don't want the hooks to be run twice, and it takes a couple of seconds. For this reason, ops will run the hooks before executing ops apply --auto-approve, but it will not run the hooks again before running terraform apply, or before running terraform init ....

Secrets in hooks

"Before hooks" are always executed before secrets are loaded. If you would like a before hook to have access to secrets, create an action with load_secrets: true and call the action from a before hook.