Container healthcheck integration
Tags:
How-to
If you want to use the healthcheck feature for a container.
You can inspect a container with docker inspect $CONTAINER_NAME.
The response is an array with one JSON object:
[
{
"Id": "CONTAINER_ID",
"Created": "2021-11-09T21:18:05.552662745Z",
"Path": "/start.py",
"Args": [],
"State": {
"Status": "running",
"Running": true,
"Paused": false,
"Restarting": false,
"OOMKilled": false,
"Dead": false,
"Pid": 12872,
"ExitCode": 0,
"Error": "",
"StartedAt": "2021-11-09T21:18:08.697693764Z",
"FinishedAt": "0001-01-01T00:00:00Z",
"Health": {
"Status": "healthy",
"FailingStreak": 0,
"Log": [
{
"Start": "2021-11-10T18:51:32.122181664Z",
"End": "2021-11-10T18:51:32.304082149Z",
"ExitCode": 0,
"Output": "OK"
}
]
}
},
"Image": "IMAGE_SH"
"HostConfig": {
...
},
"GraphDriver": {
...
},
"Mounts": [
...
],
"Config": {
"Hostname": "hostname",
"Domainname": "",
"User": "",
"AttachStdin": false,
"AttachStdout": false,
"AttachStderr": false,
"ExposedPorts": {
"8008/tcp": {},
"8009/tcp": {},
"8448/tcp": {}
},
"Tty": false,
"OpenStdin": false,
"StdinOnce": false,
"Env": [
...
],
"Cmd": null,
"Healthcheck": {
"Test": [
"CMD-SHELL",
"curl -fSs http://localhost:8008/health || exit 1"
],
"Interval": 60000000000,
"Timeout": 5000000000
},
"Image": "IMAGE_NAME",
"Volumes": {
"/data": {}
},
"WorkingDir": "",
"Entrypoint": [
"/start.py"
],
"OnBuild": null,
"Labels": {
...
}
},
"NetworkSettings": {
...
}
}
]
If you take a look at the object, you will find the healthcheck cmd.
curl -fSs http://localhost:8008/health || exit 1
Check the curl docs, how the options return a nice result. Now what you can do, you can search for it using grep:
docker inspect $CONTAINER_NAME | grep "healthy"
"Status": "healthy",
The problem in this case is, you want a boolean result. So you have different option, you can handle this case with option -o of the grep search:
docker inspect docker_synapse_1 | grep -o "healthy"
"healthy"
Okay cool, let’s check the exit code. echo $? will return 0, so know you can use this pipe in a shell script and handle if conditions.
As you may know, we are not the only one with this problem. So Docker provides a convenient solution.
Docker inspect provides the option –format, which allows us to ask for a specified JSON structure. It can do more, but for our case it is enough.
docker inspect --format '{{.State.Health.Status }}' $CONTAINER_NAME
The command above will return healthy.
if you want the double quotes, you can add json after the curly brackets, like {{json .State...}}.
So there you have it, you can now check against this string using grep or just [[ $? != "healthy"]].
Advantages:
- No pipe required.
- Returning the exact value of the object key.
- Just Docker, no strings attached.
Last but not least
If the post is updated, the creation date, will be pushed. So it might happend, you see an existing page back on frontpage. I think, this approach is valid, so wrong information or gained information is covered. But if I am going to write a new part of topic, I might include an updated link to the new post.
Home