envoy-preflight is a simple wrapper application which makes it easier to run applications which depend on envoy as a sidecar container for outside network access. It ensures that your application doesn't start until envoy is ready, and that envoy shuts down when the application exits. It is best used as a prefix to your existing Docker entrypoint. It executes any argument passed to it, doing a simple path lookup:
envoy-preflight echo "hi"
envoy-preflight /bin/ls -a
The envoy-preflight wrapper won't do anything special unless you provide at least the ENVOY_ADMIN_API environment variable. This makes, e.g., local development of your app easy.
If you do provide the ENVOY_ADMIN_API environment variable, envoy-preflight
will poll the proxy indefinitely with backoff, waiting for Envoy to report itself as live. This implies it has loaded cluster configuration (for example from an ADS server). Only then will it execute the command provided as an argument, so that your app can immediately start accessing the outside network.
All signals are passed to the underlying application. Be warned that SIGKILL cannot be passed, so this can leave behind a orphaned process.
When the application exits, as long as it does so with exit code 0, envoy-preflight will instruct envoy to shut down immediately.