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Simple Health Check for Docker
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Docker Health Check

I run Docker both in production on CentOS, and also run it on my Macs for development and testing. Recently, I noticed some weird behavior on my Mac's version of Docker where sometimes containers would stop responding to inbound TCP connections, but otherwise behave normally. (This is the bug I filed...) I built this test suite to catch that behavior as it happens, and see what changes I could make to prevent that behavior.


bash <(curl -s [ PORT ]

If a port is specified as an argument, it will be listned on, otherwise the default port of 8123 will be used.

If Docker is not running or in the process of starting up, the script will try to start the container once per second until it succeeds. Once it succeeds, testing will immediately commence.

Testing consists of running curl against the Nginx container once per second, and writing the first line of output to a file named results-YYYYMMDDTHHMMSS.log.

If the container is killed (or Docker is stopped), the script will try to restart the container once per second until it succeeds, then resume testing, with the results going to a new file.

Interpreting Results

To see the results of tests, run wc -l results-*. Example:

wc -l results-*
      19 results-20190505T135448.log
      60 results-20190505T135605.log
    8570 results-20190505T135711.log

The timestamp on the file will tell when the test was started, and the number of lines will tell how many seconds nginx responded for. In this case, there were a few short-lived tests and then a test that ran for well over two hours.

In the failure scenario that I had when originally writing this test, Docker containers would stop responding to TCP traffic within 30 minutes, yet I could docker run -it ID bash and connect to those containers, and run curl from them, etc.


My email is I am also @dmuth on Twitter and Facebook!

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