# Instance Configuration via `cloud-config`

This set of modules creates specialized [cloud-config](https://cloud.google.com/container-optimized-os/docs/how-to/run-container-instance#starting_a_docker_container_via_cloud-config) configurations, which are designed for use with [Container Optimized OS](https://cloud.google.com/container-optimized-os/docs) (the [onprem module](./onprem/) is the only exception) but can also be used as a basis for other image types or cloud providers.

These modules are designed for several use cases:

- to quickly prototype specialized services (eg MySQL access or HTTP serving) for prototyping infrastructure
- to emulate production services for perfomance testing
- to easily add glue components for services like DNS (eg to work around inbound/outbound forwarding limitations)
- to implement cloud-native production deployments that leverage cloud-init for configuration management, without the need of a separate tool

## Available modules

- [CoreDNS](./coredns)
- [MySQL](./mysql)
- [Nginx](./nginx)
- [On-prem in Docker](./onprem)
- [Squid forward proxy](./squid)

## Using the modules

All modules are designed to be as lightweight as possible, so that specialized modules like [compute-vm](../compute-vm) can be leveraged to manage instances or instance templates, and to allow simple forking to create custom derivatives.

Modules use Docker's [Google Cloud Logging driver](https://docs.docker.com/config/containers/logging/gcplogs/) by default, so projects need to have the logging API enabled. If that's not desirable simply remove `--log-driver=gcplogs` from the relevant systemd unit in `cloud-config.yaml`.

To use the modules with instances or instance templates, simply set use their `cloud_config` output for the `user-data` metadata. When updating the metadata after a variable change remember to manually restart the instances that use a module's output, or the changes won't effect the running system.

For convenience when developing or prototyping infrastructure, an optional test instance is included in all modules. If it's not needed, the linked `*instance.tf` files can be removed from the modules without harm.

## TODO

- [ ] convert all `xxx_config` variables to use file content instead of path