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Polishing Varnish

Polishing Varnish

Talk on Varnish given by Adam Horwich, Systems Engineer, at MetaBroadcast on August 14th, 2013.

MetaBroadcast

August 14, 2013
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  1. Cloud Resilience • Resilient Active/Active Varnish • Storage Backends •

    ELBs vs. Route53 DNS - When to use • Availability Zones • SSL Internal Facing (faster) Public Facing (SSL) Tuesday, 3 September 13
  2. Gracefully Done • Serving graceful content is hacky • Has

    poor documentation • Varnish is a little buggy • But it makes clients happy Tuesday, 3 September 13
  3. Marrying Graceful Behaviour with Cloud Resilience • Headaches! • TTL

    inheritance, DNS records • Failure modes! • Faking a fetch from secondary • Persistence! • Using file or persistent storage depending on requesting service Tuesday, 3 September 13
  4. Gracefully Denying Service • Your refreshing process needs to be

    courteous • Originally a subprocess spawning cURL • Dangerous if you have scheduled services connected to Varnish • Now using Python Twisted to enable queues and concurrency Tuesday, 3 September 13
  5. Logging for your Grace • Deferred Semaphore requests can queue

    • You may want to monitor for slow queries • Limitations in using Twisted Agent request • Next iteration will have timeout handling Submitted: 2013-08-14 11:40:44.413821 Started: 2013-08-14 11:40:44.413927 Completed: 2013-08-14 11:40:44.513366 http://localhost/query Tuesday, 3 September 13