Technical details

build

When building the image, the script /usr/libexec/container-setup.sh gets called
This script creates data / config directories and sets their permissions accordingly

When running the image, the script /usr/bin/container-entrypoint.sh acts as a container entrypoint
The entrypoint first checks if it's in an OpenShift / Kubernetes environment by inspecting the ENV variable POD_NAMESPACE
- If POD_NAMESPACE is set, the entrypoint runs the command /usr/bin/peer-finder which looks for other nodes. peer-finder then calls the script /usr/share/container-scripts/mysql/configure-galera.sh which creates a galera-config at /etc/my.cnf.d/galera.cnf
Next, the entrypoint checks if the directory /var/lib/mysql/mysql exists. If not, it assumes that mysql needs to be set up, thus it calls the script /usr/share/container-scripts/mysql/configure-mysql.sh
- This script creates a fist time mysql config which sets up users, tables, etc.
After that, the entrypoint calls mysqld with correct flags to run mysqld

The readinessProbe lives in /usr/share/container-scripts/mysql/readiness-probe.sh, if the script exits with 0, the container is ready, other error codes are interpreted as notReady

peer-finder is a go binary which finds all pods of a service. The source can be found here: https://github.com/kubernetes/contrib/tree/master/peer-finder
It can be compiled like this:

$ go get -v
$ CGO_ENABLED=0 go build -a -installsuffix cgo --ldflags '-w' ./peer-finder.go