HAProxy Enterprise Documentation 2.5r1

Cache

A cache section enables caching of responses from backend servers. The cache resides in memory and does not store state on the filesystem, which means that it will not persist beyond a reload.

Cache limitations

The cache won't store and won't deliver objects in these cases:

  • If the response is not a 200

  • If the response contains a Vary header

  • If the Content-Length and the size of the headers is greater than max-object-size

  • If the response is not cacheable

  • If the request is not a GET

  • If the HTTP version of the request is smaller than 1.1

  • If the request contains an Authorization header

Cache section examples

In the following configuration sample, we define a cache section labeled mycache and adjust the total cache memory size, the maximum size of a single item in the cache, and how long an item should live in the cache.

cache mycache
   # Total size of the cache in MB
   total-max-size 4

   # Max size of any single item in bytes
   max-object-size 10

   # Time to live for each item in seconds
   # This can be overridden with a Cache-Control header
   max-age 30

When the load balancer serves a cached item, it can return the response directly to the client without needing to contact the backend server. To use the defined cache we add the http-response cache-store directive on our backend section and the http-request cache-use directive to use cached responses.

cache mycache
   total-max-size 4095
   max-object-size 10000
   max-age 30

backend servers
   # Use mycache for all requests
   http-request cache-use mycache

   # Store http requests in cache
   http-response cache-store mycache

   server s1 192.168.1.25:80 check
   server s2 192.168.1.26:80 check

Conditionally caching requests

Often, caching all responses is unnecessary. You can select which resources to cache by using an if statement on the http-request cache-use directive.

Use the path_beg fetch to check whether the requested path begins with /api/ and only cache the response if it does:

cache mycache
   total-max-size 4095
   max-object-size 10000
   max-age 30

backend servers
   # Use mycache if the request path begins with /api/
   http-request cache-use mycache if { path_beg /api/ }
   http-response cache-store mycache
   server s1 192.168.1.25:80 check
   server s2 192.168.1.26:80 check

See also

Caching

Next up

Http-errors