Proxy Caching plugin

This plugin provides a reverse proxy cache implementation for IAM. It caches response entities based on configurable response code and content type, as well as request method. It can cache per-Consumer or per-API. Cache entities are stored for a configurable period of time, after which subsequent requests to the same resource will re-fetch and re-store the resource. Cache entities can also be forcefully purged via the Admin API prior to their expiration time.

Terminology

plugin: a plugin executing actions inside IAM before or after a request has been proxied to the upstream API.
Service: the IAM entity representing an external upstream API or microservice.
Route: the IAM entity representing a way to map downstream requests to upstream services.
Consumer: the IAM entity representing a developer or machine using the API. When using IAM, a Consumer only communicates with IAM which proxies every call to the said upstream API.
Credential: a unique string associated with a Consumer, also referred to as an API key.
upstream service: this refers to your own API/service sitting behind IAM, to which client requests are forwarded.
API: a legacy entity used to represent your upstream services. Deprecated in favor of Services.

Configuration

Enabling the plugin on a Service

With a database

Configure this plugin on a Service by making the following request:

$ curl -X POST http://localhost:8001/services/{service}/plugins \
    --data "name=proxy-cache"  \
    --data "config.strategy=memory"

Without a database

Configure this plugin on a Service by adding this section do your declarative configuration file:

plugins:
- name: proxy-cache
  service: {service}
  config:
    strategy: memory

In both cases, {service} is the id or name of the Service that this plugin configuration will target.

Enabling the plugin on a Route

With a database

Configure this plugin on a Route with:

$ curl -X POST http://localhost:8001/routes/{route}/plugins \
    --data "name=proxy-cache"  \
    --data "config.strategy=memory"

Without a database

Configure this plugin on a Route by adding this section do your declarative configuration file:

plugins:
- name: proxy-cache
  route: {route}
  config:
    strategy: memory

In both cases, {route} is the id or name of the Route that this plugin configuration will target.

Enabling the plugin on a Consumer

With a database

You can use the http://localhost:8001/plugins endpoint to enable this plugin on specific Consumers:

$ curl -X POST http://localhost:8001/consumers/{consumer}/plugins \
    --data "name=proxy-cache" \
     \
    --data "config.strategy=memory"

Without a database

Configure this plugin on a Consumer by adding this section do your declarative configuration file:

plugins:
- name: proxy-cache
  consumer: {consumer}
  config:
    strategy: memory

In both cases, {consumer} is the id or username of the Consumer that this plugin configuration will target.

You can combine consumer_id and service_id

in the same request, to furthermore narrow the scope of the plugin.

Global plugins

Using a database, all plugins can be configured using the http://localhost:8001/plugins/ endpoint.
Without a database, all plugins can be configured via the plugins: entry on the declarative configuration file.

A plugin which is not associated to any Service, Route or Consumer (or API, if you are using an older version of IAM) is considered "global", and will be run on every request. Read the Plugin Reference and the Plugin Precedence sections for more information.

Parameters

Here's a list of all the parameters which can be used in this plugin's configuration:

form parameter	description
`name`	The name of the plugin to use, in this case `proxy-cache`
`service_id`	The id of the Service which this plugin will target.
`route_id`	The id of the Route which this plugin will target.
`enabled` default value: `true`	Whether this plugin will be applied.
`consumer_id`	The id of the Consumer which this plugin will target.
`api_id`	The id of the API which this plugin will target. Note: The API Entity is deprecated in favor of Services.
`config.response_code` default value: 200, 301, 404	Upstream response status code considered cacheable
`config.request_method` default value: GET, HEAD	Downstream request methods considered cacheable
`config.content_type` default value: text/plain, application/json	Upstream response content types considered cacheable. The plugin performs an exact match against each specified value; for example, if the upstream is expected to respond with a `application/json; charset=utf-8` content-type, the plugin configuration must contain said value or a `Bypass` cache status will be returned
`config.vary_headers` optional	Relevant headers considered for the cache key. If undefined, none of the headers are taken into consideration.
`config.vary_query_params` optional	Relevant query parameters considered for the cache key. If undefined, all params are taken into consideration.
`config.cache_ttl` default value: 300	TTL, in seconds, of cache entities
`config.cache_control` default value: false	When enabled, respect the Cache-Control behaviors defined in RFC7234
`config.storage_ttl` optional	Number of seconds to keep resources in the storage backend. This value is independent of `cache_ttl` or resource TTLs defined by Cache-Control behaviors.
`config.strategy`	The backing data store in which to hold cache entities. Accepted values are; `memory`, and `redis`.
`config.memory.dictionary_name` default value: kong_cache	The name of the shared dictionary in which to hold cache entities when the memory strategy is selected. Note that this dictionary currently must be defined manually in the IAM Nginx template.
`config.redis.host` semi-optional	Host to use for Redis connection when the redis strategy is defined
`config.redis.port` semi-optional	Port to use for Redis connection when the redis strategy is defined
`config.redis.timeout` semi-optional default value: 2000	Connection timeout to use for Redis connection when the redis strategy is defined
`config.redis.password` semi-optional	Password to use for Redis connection when the redis strategy is defined. If undefined, no AUTH commands are sent to Redis.
`config.redis.database` semi-optional default value: 0	Database to use for Redis connection when the redis strategy is defined
`config.redis.sentinel_master` semi-optional	Sentinel master to use for Redis connection when the redis strategy is defined. Defining this value implies using Redis Sentinel.
`config.redis.sentinel_role` semi-optional	Sentinel role to use for Redis connection when the redis strategy is defined. Defining this value implies using Redis Sentinel.
`config.redis.sentinel_addresses` semi-optional	Sentinel addresses to use for Redis connection when the redis strategy is defined. Defining this value implies using Redis Sentinel.
`config.redis.cluster_addresses` semi-optional	Cluster addresses to use for Redis connection when the `redis` strategy is defined. Defining this value implies using Redis cluster.

Strategies

kong-plugin-enterprise-proxy-cache is designed to support storing proxy cache data in different backend formats. Currently the following strategies are provided:

memory: A lua_shared_dict. Note that the default dictionary, kong_cache, is also used by other plugins and elements of IAM to store unrelated database cache entities. Using this dictionary is an easy way to bootstrap the proxy-cache plugin, but it is not recommended for large-scale installations as significant usage will put pressure on other facets of IAM's database caching operations. It is recommended to define a separate lua_shared_dict via a custom Nginx template at this time.
redis: Supports Redis and Redis Sentinel deployments.

Cache Key

IAM keys each cache elements based on the request method, the full client request (e.g., the request path and query parameters), and the UUID of either the API or Consumer associated with the request. This also implies that caches are distinct between APIs and/or Consumers. Currently the cache key format is hard-coded and cannot be adjusted. Internally, cache keys are represented as a hexadecimal-encoded MD5 sum of the concatenation of the constituent parts. This is calculated as follows:

key = md5(UUID | method | request)

Where method is defined via the OpenResty ngx.req.get_method() call, and request is defined via the Nginx $request variable. IAM will return the cache key associated with a given request as the X-Cache-Key response header. It is also possible to precalculate the cache key for a given request as noted above.

Cache Control

When the cache_control configuration option is enabled, IAM will respect request and response Cache-Control headers as defined by RFC7234, with a few exceptions:

Cache revalidation is not yet supported, and so directives such as proxy-revalidate are ignored.
Similarly, the behavior of no-cache is simplified to exclude the entity from being cached entirely.
Secondary key calculation via Vary is not yet supported.

Cache Status

IAM identifies the status of the request's proxy cache behavior via the X-Cache-Status header. There are several possible values for this header:

Miss: The request could be satisfied in cache, but an entry for the resource was not found in cache, and the request was proxied upstream.
Hit: The request was satisfied and served from cache.
Refresh: The resource was found in cache, but could not satisfy the request, due to Cache-Control behaviors or reaching its hard-coded cache_ttl threshold.
Bypass: The request could not be satisfied from cache based on plugin configuration.

Storage TTL

IAM can store resource entities in the storage engine longer than the prescribed cache_ttl or Cache-Control values indicate. This allows IAM to maintain a cached copy of a resource past its expiration. This allows clients capable of using max-age and max-stale headers to request stale copies of data if necessary.

Upstream Outages

Due to an implementation in IAM's core request processing model, at this point the proxy-cache plugin cannot be used to serve stale cache data when an upstream is unreachable. To equip IAM to serve cache data in place of returning an error when an upstream is unreachable, we recommend defining a very large storage_ttl (on the order of hours or days) in order to keep stale data in the cache. In the event of an upstream outage, stale data can be considered “fresh” by increasing the cache_ttl plugin configuration value. By doing so, data that would have been previously considered stale is now served to the client, before IAM attempts to connect to a failed upstream service.

Admin API

This plugin provides several endpoints to managed cache entities. These endpoints are assigned to the proxy-cache RBAC resource.

The following endpoints are provided on the Admin API to examine and purge cache entities:

Retrieve a Cache Entity

Two separate endpoints are available: one to look up a known plugin instance, and another that searches all proxy-cache plugins data stores for the given cache key. Both endpoints have the same return value.

Endpoint

/proxy-cache/:plugin_id/caches/:cache_id

Attributes	Description
`plugin_id`	The UUID of the proxy-cache plugin
`cache_id`	The cache entity key as reported by the X-Cache-Key response header

Endpoint

/proxy-cache/:cache_id

Attributes	Description
`cache_id`	The cache entity key as reported by the X-Cache-Key response header

Response

If the cache entity exists

HTTP 200 OK

If the entity with the given key does not exist

HTTP 400 Not Found

Delete Cache Entity

Endpoint

/proxy-cache/:plugin_id/caches/:cache_id

Attributes	Description
`plugin_id`	The UUID of the proxy-cache plugin
`cache_id`	The cache entity key as reported by the `X-Cache-Key` response header

Endpoint

/proxy-cache/:cache_id

Attributes	Description
`cache_id`	he cache entity key as reported by the `X-Cache-Key` response header

Response

If the cache entity exists

HTTP 204 No Content

If the entity with the given key does not exist

HTTP 400 Not Found

Purge All Cache Entities

Endpoint

/proxy-cache/

Response

HTTP 204 No Content

Note that this endpoint purges all cache entities across all proxy-cache plugins.