redeploying this blog via nixpacks and dokploy. i learned of dokploy via this HN thread about a different platform called dokku.
i'm not really well-versed in devops, so this was a bit of a struggle. in the end though it came down to:
making various application options configurable. i figured the easiest way to configure the app was via environment variables, which i usually eschew in favor of config files. the reason i didn't use a config file this time is because i don't know how to deploy a config file to the home directory of the app on application deployment. a data volume must be defined for persistence, which would include the config file, but the location of it would have been to be defined in the config file itself (no hardcoded paths, duh). next i was too lazy to figure out how to pass additional startup parameters via the nixpacks config, because the obvious solution were enviroment variables.
the other problem was getting the JDK version for the build right, as i didn't realize that the same image (i.e. same JDK) for building the app is also used for running it (which makes perfect sense). selection of the JDK version happens via an environment variable, but i was looking for a dedicated area for defining env's for the build. once the penny dropped it just took a single line in the environment config and a redeployment to run it on JDK-21.