# The cache-config relation The `cache-config` interface connects the Ingress Configurator charm (requirer) to the [Content Cache](https://charmhub.io/content-cache) charm (provider). It configures the Content Cache charm with backend origins, healthcheck parameters, and caching rules so that HAProxy can route traffic through Content Cache. ## Databag fields The Ingress Configurator charm writes the following fields to its **application databag**: | Field | Type | Required | Description | |----------------------------|------------------------|------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | `backends` | JSON array of strings | Yes | List of backend URLs (e.g. `["http://10.0.0.1:8080"]`) that content-cache should proxy. | | `backend_hostname` | string | No | Hostname content-cache presents (SNI and HTTP `Host` header) when connecting to the origin backend over HTTPS. Required when `backend-protocol` is `https`. Sourced from the `cache-backend-hostname` config; unrelated to and never derived from `hostname`. content-cache passes this to nginx as `proxy_ssl_name` and `proxy_set_header Host`. | | `fail_timeout` | string | Yes | Time after which a backend is marked unavailable following a failure (e.g. `"30s"`). | | `healthcheck_interval` | string | Yes | Healthcheck interval in milliseconds (e.g. `"10000"` for 10 s). | | `healthcheck_path` | string | Yes | URL path used for healthchecks (e.g. `"/"`). | | `healthcheck_valid_status` | JSON array of integers | Yes | HTTP status codes that indicate a healthy backend (e.g. `[200]`). | | `healthcheck_ssl_verify` | JSON boolean | Yes | Whether nginx should verify the backend TLS certificate during healthchecks. | | `proxy_cache_valid` | JSON array of strings | Yes | Cache validity rules in nginx format (e.g. `["200 1h"]`). An empty array emits no `proxy_cache_valid` directives, so caching defers to the `Cache-Control` and `Expires` headers of the backend. | `backend_hostname` is sourced from the `cache-backend-hostname` charm config, which is normally left unset for HTTP backends – content-cache passes the incoming `Host` header through unchanged in that case. Setting `cache-backend-hostname` changes the `Host` header the backend receives on every request, so only set it when the backend application is aware it’s being fronted by a cache (e.g. its own hostname allowlist or CORS configuration accepts this value). The Content Cache charm writes the following field to its **unit databag**: | Field | Type | Description | |-----------------|--------|--------------------------------------------------------------------------------------------------------------------------------------------------------------| | `cache-backend` | string | URL on which Content Cache is reachable (e.g. `"https://10.1.0.5:30000"`). Ingress Configurator uses this to redirect HAProxy traffic through Content Cache. |