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Using Exit Stack Traces for Debugging

--trace-exit CLI option will print a stack trace on every proactive process.exit invocation. It is convenient to confirm if the abnormal exit of the process was initiated from an invocation of process.exit or something other crashes.

Caveat: --trace-exit CLI option is available since Node.js v13.5.0.

How To

There are conditions that we used an third party library that we have trivial knowledge of the implementation details. It is hard to determine where the exit is trigger in which library in these conditions. On the first step we have to determine if it is a proactive process.exit invocation and where it is to prevent follow up not trivial work of detailed digging the exit reasons.

The simple step is to add an option --trace-exit on starting the Node.js process. Since then, we can see a stacktrace on each call of process.exit.

 > node --trace-exit src/abnormal-exit.js
(node:26480) WARNING: Exited the environment with code 0
    at exit (internal/process/per_thread.js:168:13)
    at /node_modules/some-obscure-library:199:32 # this is the actual location.
    at Module._compile (internal/modules/cjs/loader.js:1139:30)
    at Module._extensions..js (internal/modules/cjs/loader.js:1159:10)
    at Module.load (internal/modules/cjs/loader.js:988:32)
    at Module._load (internal/modules/cjs/loader.js:896:14)
    at executeUserEntryPoint (internal/modules/run_main.js:71:12)

With the knowledge of where the calls of process.exit is, we can check around the invocation to understand the reasons and prevent it from abnormal exits.

If the process doesn't output a stack trace on exit, we can come to a conclusion that the process exited for other reasons, and we can deploy strategy according to the abnormal termination guides on common symptoms.

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