swaperooni

Hot-reload a child process without tearing down the parent PID. Proxies signals into the child process.

• if the child exits, swaperooni exits with the same code.
• if a swap request is issued, the child is torn down, and new child brought up.

Supports two hot-reload request options:

• ipc - send a newline delimited command string from the child to the swaperooni socket. See examples/ipc_bash_hopscotch/main.sh.
• poll - monitor the mtime of a file. on change, re-execute it.

swaperooni is not a supervisor. swaperooni is similar to tini.

Why

Because you can. Generally, avoid using this, and use a supervisor/orchestrator. You may have cases where swapping child PIDs is more desirable (e.g. oddball docker/k8s environments).

How

See the examples.

• SOCKET_PATH=demo.sock cargo run ipc -- bash examples/ipc_bash_hopscotch/a.sh
  • program a runs momentarily, then requests to be swapped for program b. b requests program c, and c gracefully exits.
• SOCKET_PATH=demo.sock cargo run ipc -- node examples/ipc_node_counter/index.mjs 0
  • run a node.js process. the process asks swaperooni to run itself again, but with different params (a counter)
• cargo run poll --poll-interval-ms=1000 -- examples/poll_countdown/main.sh 5
  • poll for entrypoint change and re-run it.

Performance

Well, it is <1MB and does nothing most of the time.