Comment on Notice: failed container health check for example.org

• irmadlad@lemmy.world ⁨4⁩ ⁨hours⁩ ago

  Still learning on this journey of self hosting

  No worries mate. I bet if we all posted some of the boners even seasoned selfhosters have pulled, it would make a hilarious book for nerds and geeks. Sometimes I think, ‘gosh I sure am glad there wasn’t anyone around to see that!’

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• cecilkorik@lemmy.ca ⁨18⁩ ⁨hours⁩ ago

  The purpose of the health check is to allow docker itself to talk to whatever service is running on the container to make sure it’s always responding happily, connected to everything it needs to be connected to for proper operation, and is not overloaded or stuck somehow.

  Docker does this by pretending to be a web browser, and going to the specified “health check URL”. The key thing I think you’re missing here is that the health check URL is supposed to be a URL that, ideally, runs on your container and does some meaningful checks on the health of your service, or at the very least, proves that when you connect to it, it is able to serve up a working static page or login page or something (which doesn’t actually prove it’s working completely, but is often good enough)

  Now, you’re probably wondering why this isn’t automatic, and the answer is because there’s no standard “health check URL” that fits all services. Not all services even respond to URLs at all, and the ones that do may have different URLs for their health checks, they may need different hostnames to be used, etc.

  By setting health check URL to example.com, basically what you’re doing is constantly testing whether the real-world website example.com way over there somewhere is working, and as long as it is, docker assumes your container is fine. Which it might be, or it might not be, it has no idea and you have no idea, because it’s not even attempting to connect to the container at all, it’s going to the URL you specified, which is way out there on the internet somewhere, and this effectively does nothing useful for you.

  It’s understandable why you probably thought this made sense, that it was testing network connectivity or something, but that is not the purpose of the health check URL, and if you don’t have a meaningful URL to check, you can probably just omit or disable the healthcheck in this case. Docker only uses it to decide if it needs to restart the container or alert you of the failure.

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  • Pete90@feddit.org ⁨8⁩ ⁨hours⁩ ago

    Thank you so much for your detailed answer. That brought me up to speed. I just never questioned it and, as you said, assumed that it was to test network connectivity.

    It also finally explains the issues with those containers I kept having every few months. It always fixed itself before I had the time to actually look into it, but it has always been bugging me. This time I was able to actually catch it.

    I’ll update the health checks to the proper URL im using, or should I use localhost:port?

    Anyway, thanks again!

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• ramielrowe@lemmy.world ⁨18⁩ ⁨hours⁩ ago

  If the container you’re hosting has a http web service on say port 8080, then you’d want to curl something at localhost:8080. The particular URL/path you hit will depend on the app. If the app is particularly cloud-y, it might even have a specific endpoint for health checking by a container platform. If you share the name of the app I might be able to point you in the right direction.

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  • Pete90@feddit.org ⁨8⁩ ⁨hours⁩ ago

    Ah, that makes sense, thanks for clearing it up for me. It’s several containers but now that I know what I’m looking for, I’ll be able to figure it out. I was just living in blissful ignorance until now.

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