Flagon

Query flags on the command line

Why?

The main reason for developing this is so that I can use feature flags in the CI processes; to allow migration between different steps and ways of doing different tasks, with control over which users/branches/changes see which versions of a task.

The second reason is for debugging: Is a particular flag on or off for a given user? By having this in a CLI tool, this information can be embedded in practically any system.

Usage

> flagon state "some-flag-name" --user "${user_id}" --attr "branch=${branch}"
# { "name": "some-flag-name", "defaultValue": false, "value": true }

Flagon's exit codes are as follows:

• 0 the flag queried is on (true)
• 1 the flag queried is off (false)
• 2 an error occurred querying the flag

If you need flagon state`` to always succeed, use || true`:

json=$(flagon state "some-flag-name" --user "${user_id}" --attr "branch=${branch}" || true)

By default, the output is the json of the flag struct. You can also use --output template=<GO TEMPLATE> to customise the output, which is useful when exporting the status as environment variables (or outputs) in CI systems:

> flagon state "some-flag-name" --output "template={{ .Value }}" || true
# true

In CI systems, it is often useful to control flags based on the committer, or the branch they are pushing. For example, this can be done by querying git:

email=$(git show --quiet --pretty="format:%ce")
branch=$(git rev-parse --abbrev-ref HEAD)

if flagon state "ci-replacement-deploy" --user "${email}" --attr "branch=${branch}" --silent; then
  ./build/replacement-deploy.sh "${branch}" "${commit}"
else
  ./build/deploy.sh "${branch}" "${commit}"
fi

The --user flag should always map to the identifier for the user in the flag backend, for example, in LaunchDarkly, this maps to the user's key property:

flagon state "ci-replacement-deploy" --user "${user_id}"

You can also pass in other attributes:

flagon state "ci-replacement-deploy" --user "${user_id}" --attr "email=${email}"

Github Actions

Add pondidum/flagon as a step in your job, and the flagon binary will be available on your $PATH in subsequent steps:

steps:
- name: Configure Flagon
  uses: pondidum/flagon@main

- name: Run Script
  run: |
    if flagon state "enable-script" false --attr branch="${{ github.ref_name }}"; then
      ./some-script.sh
    fi

Optionally, you can specify which version of flagon to use, otherwise the latest release is used:

steps:
- name: Configure Flagon
  uses: pondidum/flagon@main
  with:
    version: 0.0.5

You can also use flagon to control if jobs (or steps) run. This uses the --output template feature to print just the value of the flag's .Value property:

jobs:
  flags:
    runs-on: ubuntu-latest

    outputs:
      enabled: ${{ steps.query.outputs.enabled }}

    steps:
    - name: Configure Flagon
      uses: pondidum/flagon@main

    - name: Query
      id: query
      run: echo "enabled=$(flagon state "enable-extra-job" false --output "template={{ .Value }}")" >> "${GITHUB_OUTPUT}"

  controlled:
    runs-on: ubuntu-latest
    if: ${{ needs.flags.outputs.enabled }}
    needs:
      - flags

    steps:
    - name: Print
      run: echo "${{ needs.flags.outputs.enabled }}"

Backends

Currently, this only supports LaunchDarkly as a backend. I am open to Pull Requests or suggestions of other backends to add.

Configuration

Common

Flag	Default	Description
--backend	launchdarkly	The backend to query flags from
--output	json	The output format to write to the console. Currently only supports json
--silent	false	Silence any console output

Telemetry

EnvVar	Default	Description
OTEL_TRACE_EXPORTER		Which exporter to use: otlp, stdout, stderr
OTEL_EXPORTER_OTLP_ENDPOINT	localhost:4317	Set the Exporter endpoint
OTEL_EXPORTER_OTLP_TRACES_ENDPOINT		Set the Exporter endpoint, takes priority over OTEL_EXPORTER_OTLP_ENDPOINT
OTEL_EXPORTER_OTLP_HEADERS		A Csv of Headers and Values to pass to the tracing service, for example Authentication: Bearer 13213213,X-Environment: Production
OTEL_DEBUG	false	Print debug information from tracing to the console

Backend: LaunchDarkly

EnvVar	Flag	Default	Description
FLAGON_LD_SDKKEY	--ld-sdk-key		The project SDK Key to use
FLAGON_LD_TIMEOUT	--ld-timeout	10s	How long to wait for successful connection
FLAGON_LD_DEBUG	--ld-debug	0	Set to true (or 1) to see debug information from the LaunchDarkly client