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envoy-preflight

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.

Environment variables

Variable Purpose
ENVOY_ADMIN_API This is the path to envoy's administration interface, in the format http://127.0.0.1:9010. If provided, envoy-preflight will poll this url at /server_info waiting for envoy to report as LIVE. If provided and local (127.0.0.1 or localhost), then envoy will be instructed to shut down if the application exits cleanly.
ENVOY_KILL_API This is the endpoint of the POST command to kill envoy, which defaults to $ENVOY_ADMIN_API/quitquitquit, but you can provide any value in format http://127.0.0.1:9010/quitquitquit. This can be used to support istio by providing the pilot-agent port.
NEVER_KILL_ENVOY If provided and set to true, envoy-preflight will not instruct envoy to exit under any circumstances.
ALWAYS_KILL_ENVOY If provided and set to true, envoy-preflight will instruct envoy to exit, even if the main application exits with a nonzero exit code.
START_WITHOUT_ENVOY If provided and set to true, envoy-preflight will not wait for envoy to be LIVE before starting the main application. However, it will still instruct envoy to exit.