Memcached Service

Memcached is an in-memory key-value store used for caching by many web applications and frameworks. It is available in Stackato as a service which can be shared by application instances.

Using the Service

As with other data services, the location and port of the memcached service is exposed to the application via environment variables: MEMCACHE_URL or VCAP_SERVICES.

The easiest way to connect an application to a Memcached service is to use the MEMCACHE_URL environment variable. It contains the location and port of the service created for the application. For example:

MEMCACHE_URL=10.13.0.6:11000

Using MEMCACHE_URL will only work if sasl_enabled is set to False in the memcached_node configuration (default). To enable SASL for Memcached, a Stackato administrator can run the following commands on the Cloud Controller:

$ kato config set memcached_node sasl_enabled true
$ kato restart memcached_node

With SASL enabled, applications must parse the STACKATO_SERVICES or VCAP_SERVICES environment variables to extract the "name", "user", and "password" strings from the memcached "credentials" list. Using SASL with Memcached requires client libraries/modules in the application which support authentication via SASL.

Warning

Running Memcached without SASL enabled is insecure, and should only be done if all system users are trusted. Any Stackato user can connect to the provisioned service instance if the IP address and port is discovered.

Django Example using Memcached

The Django GTD sample application uses the simpler VCAP_SERVICES method for connecting to the Memcached service without authentication.

The relevant configuration in this example:

1. specifies the location of memcache using the MEMCACHE_URL in settings.py:

   CACHES = {
       'default': {
       'BACKEND': 'django.core.cache.backends.memcached.MemcachedCache',
       'LOCATION': os.getenv('MEMCACHE_URL'),
       }
   }
   

2. adds the cache to middleware classes:

   MIDDLEWARE_CLASSES = (
       'django.middleware.cache.UpdateCacheMiddleware',
       'django.middleware.cache.FetchFromCacheMiddleware',
       ...
   )
   

3. adds the python-memcached module and a memcached service in stackato.yml:

   requirements:
       pip:
       - python-memcached
       ...
   services:
       memcached-gtd: memcached
       ...