Docker health check command. Do we really need || exit 1?-CodePudding

There's already a similar question at What happens to a Docker Container when HEALTHCHECK fails, but the secondary point about || exit 1 was not the main focus of the question (and it hasn't been answered directly).

The Dockerfile reference contains the following example:

HEALTHCHECK
 --interval=5m --timeout=3s \
  CMD curl -f http://localhost/ || exit 1

I have seen several other examples of healthcheck instructions ending in || exit 1 around the Internet. Even when the only two possible exit codes of the original command are 0 and 1.

What's the point of || exit 1?

Wont curl -f exit on its own with error code 22? Does Docker fail to recognise error codes other than 1?

CodePudding user response：

Even when the only two possible exit codes of the original command are 0 and 1.

That's a big assumption that isn't being made by those writing the commands with || exit 1. If a command exits with a 2 or any other code except for a 0 or 1, that's undefined behavior. Presumably docker is reserving other exit codes for any additional behavior they might come up with in the future.

Specifically with curl, it can exit with a lot of other values which have a meaning for curl but would be undefined behavior for the healthcheck.