Commits on Feb 27, 2017

1. Fix memory leak in components …

   Most of our frontend apps leak memory, which causes regular Icinga
   alerts
   for 2nd line. We currently mitigate this by restarting the apps
   manually.
   
   This dashboard shows the problem:
   https://grafana.publishing.service.gov.uk/dashboard/db/memory-dashboard
   
   The primary cause of this seems to be the `GovukComponent` class. This
   currently instantiates a `ComponentResolver` class per request, which
   in turn instantiates lots of ActionView related objects.
   
   By caching the resolver for 15 minutes, we save a lot of memory.
   
   To test I've used the [derailed_benchmarks gem][derailed]. I've tested
   this with the following command on `government-frontend`:
   
   [derailed]: https://github.com/schneems/derailed_benchmarks
   
   ```
   GOVUK_APP_DOMAIN=www.gov.uk GOVUK_ASSET_ROOT=https://www.gov.uk
   GOVUK_WEBSITE_ROOT=https://www.gov.uk
   PLEK_SERVICE_CONTENT_STORE_URI=https://www.gov.uk/api
   PLEK_SERVICE_STATIC_URI=assets.publishing.service.gov.uk
   DERAILED_SKIP_ACTIVE_RECORD=true TEST_COUNT=100
   PATH_TO_HIT=/government/case-studies/nda-archive SLIMMER_DEV=1 bundle
   exec derailed exec perf:objects
   ```
   
   This makes a 100 requests to the app and outputs stats on memory usage.
   
   Before this change (master):
   
   ```
   Total allocated: 159341340 bytes (1415052 objects)
   Total retained:  680097 bytes (5510 objects)
   ```
   
   After this change:
   
   ```
   Total allocated: 106879912 bytes (931658 objects)
   Total retained:  141145 bytes (551 objects)
   ```

   

   tijmenb committed Feb 27, 2017
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