k8S initcontainer to run envsubst

Scope

This is intended for use in the kubernetes helm chart for geOrchestra, as an initcontainer, once the datadir has been cloned (and before the pods are started).

Whaat ? Why ?

It all began with the idea to use environment variables in the datadir, wherever possible.

Thing is, while they are resolved on most of the files, there are a few cases when it isn't that smooth. Namely for now, datafeeder/frontend-config.json, the conf file for the ogc-api-records microservice for geonetwork, and more important, security-proxy/target-mappings.properties.

In the long run, it will be preferable to fix this in the apps themselves. But let's be honest, we might need that possibility from time to time anyway.

Usage

This is a very simple image. To run it, you need to

• mount the files
• declare the environment variables to use
• specify the path to the files that will be processed, in the SUBST_FILES environment variable
• run the container with an UID allowed to overwrite the files you want to process

For example,

# If you want to build it locally
docker build -t georchestra/k8s-initcontainer-envsubst .
# test it locally (replace ${FQDN} occurrences in the datafeeder config file)
docker run -u 1000:1000 -it --name envsubst --rm -v $(HOME)/dev/georchestra/datadir:/etc/georchestra -e FQDN=georchestra.mydomain.org -e SUBST_FILES="/etc/georchestra/datafeeder/frontend-config.json" georchestra/k8s-initcontainer-envsubst:latest

Important note: only the existing environment variables (i.e. the ones output by the env command) will be substituted. This includes environment variables defined to an empty string.
This means that if there are customs tokens in the ${token} format in the processed files, these will stay untouched.