Docker: Apache container with sidecar

Why would you use a sidecar?

e.g. to add something to an existing container without rewriting it.

Assuming you’ve run a container with Apache as in this post: Docker: Apache container then you’ll have an environment variable, APP_ID.

You can use this to run a sidecar container that adds a health metric. E.g.

docker run --pid=container:${APP_ID} -p 8081:8081 brendanburns/topz:db0fa58 /server --addr=

and now you have a sidecar container running. E.g.

curl localhost:8081

91 9.937410610507195 0.02218294 /server --addr=
1 0 0.0024320167 httpd -DFOREGROUND
7 0 0.005011428 httpd -DFOREGROUND
8 0 0.0008106722 httpd -DFOREGROUND
9 0 0.0009335013 httpd -DFOREGROUND



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