# Containerized Squid on Container Optimized OS

This module manages a `cloud-config` configuration that starts a containerized [Squid](http://www.squid-cache.org/) proxy on Container Optimized OS. The default configuration creates a filtering proxy that only allows connection to a whitelisted set of domains.

The resulting `cloud-config` can be customized in a number of ways:

- a custom squid.conf configuration can be set using the `squid_config` variable
- additional files (e.g. additional acls) can be passed in via the `files` variable
- a completely custom `cloud-config` can be passed in via the `cloud_config` variable, and additional template variables can be passed in via `config_variables`

The default instance configuration inserts iptables rules to allow traffic on TCP port 3128. With the default `squid.conf`, deny rules take precedence over allow rules.

Logging and monitoring are enabled via the [Google Cloud Logging driver](https://docs.docker.com/config/containers/logging/gcplogs/) configured for the Squid container, and the [Node Problem Detector](https://cloud.google.com/container-optimized-os/docs/how-to/monitoring) service started by default on boot.

The module renders the generated cloud config in the `cloud_config` output, to be used in instances or instance templates via the `user-data` metadata.

For convenience during development or for simple use cases, the module can optionally manage a single instance via the `test_instance` variable. If the instance is not needed the `instance*tf` files can be safely removed. Refer to the [top-level README](../README.md) for more details on the included instance.

## Examples

### Default Squid configuration

This example will create a `cloud-config` that allows any client in the 10.0.0.0/8 CIDR to use the proxy to connect github.com or any subdomain of github.com.

```hcl
module "cos-squid" {
  source           = "./modules/cloud-config-container/squid"
  whitelist = [".github.com"]
  clients   = ["10.0.0.0/8"]
}

# use it as metadata in a compute instance or template
resource "google_compute_instance" "default" {
  metadata = {
    user-data = module.cos-squid.cloud_config
  }
```

### Test Squid instance

This example shows how to create the single instance optionally managed by the module, providing all required attributes in the `test_instance` variable. The instance is purposefully kept simple and should only be used in development, or when designing infrastructures.

```hcl
module "cos-squid" {
  source           = "./modules/cloud-config-container/squid"
  whitelist = ["github.com"]
  clients   = ["10.0.0.0/8"]
  test_instance = {
    project_id = "my-project"
    zone       = "europe-west1-b"
    name       = "cos-squid"
    type       = "f1-micro"
    network    = "default"
    subnetwork = "https://www.googleapis.com/compute/v1/projects/my-project/regions/europe-west1/subnetworks/my-subnet"
  }
}
```


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## Variables

| name | description | type | required | default |
|---|---|:---:|:---:|:---:|
| allow | List of domains Squid will allow connections to. | <code>list&#40;string&#41;</code> |  | <code>&#91;&#93;</code> |
| clients | List of CIDR ranges from which Squid will allow connections. | <code>list&#40;string&#41;</code> |  | <code>&#91;&#93;</code> |
| cloud_config | Cloud config template path. If null default will be used. | <code>string</code> |  | <code>null</code> |
| config_variables | Additional variables used to render the cloud-config and Squid templates. | <code>map&#40;any&#41;</code> |  | <code>&#123;&#125;</code> |
| default_action | Default action for domains not matching neither the allow or deny lists | <code>string</code> |  | <code>&#34;deny&#34;</code> |
| deny | List of domains Squid will deny connections to. | <code>list&#40;string&#41;</code> |  | <code>&#91;&#93;</code> |
| file_defaults | Default owner and permissions for files. | <code title="object&#40;&#123;&#10;  owner       &#61; string&#10;  permissions &#61; string&#10;&#125;&#41;">object&#40;&#123;&#8230;&#125;&#41;</code> |  | <code title="&#123;&#10;  owner       &#61; &#34;root&#34;&#10;  permissions &#61; &#34;0644&#34;&#10;&#125;">&#123;&#8230;&#125;</code> |
| files | Map of extra files to create on the instance, path as key. Owner and permissions will use defaults if null. | <code title="map&#40;object&#40;&#123;&#10;  content     &#61; string&#10;  owner       &#61; string&#10;  permissions &#61; string&#10;&#125;&#41;&#41;">map&#40;object&#40;&#123;&#8230;&#125;&#41;&#41;</code> |  | <code>&#123;&#125;</code> |
| squid_config | Squid configuration path, if null default will be used. | <code>string</code> |  | <code>null</code> |

## Outputs

| name | description | sensitive |
|---|---|:---:|
| cloud_config | Rendered cloud-config file to be passed as user-data instance metadata. |  |

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