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Added note about DNS

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commit 77f2ea4067e70a6b2a7ead8e53ee6f136e11929a 1 parent e61e9cc
authored March 10, 2012

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@@ -132,3 +132,11 @@ You can instrument class methods, just like instance methods, using the metaprog
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 AWS::S3::Base.singleton_class.extend StatsD::Instrument
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 AWS::S3::Base.singleton_class.statsd_measure :request, 'S3.request'
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+## Reliance on DNS
+Out of the box StatsD is set up to be unidirectional fire-and-forget over UDP. Configuring the StatsD host to be a non-ip will trigger a DNS lookup (ie synchronous round trip network call) for each metric sent. This can be particularly problematic in clouds that have a shared DNS infrastructure such as AWS.
+### Common Workarounds
+1. Using an IP avoids the DNS lookup but generally requires an application deploy to change.
+2. Hardcoding the DNS/IP pair in /etc/hosts allows the IP to change without redeploying your application but fails to scale as the number of servers increases.
+3. Installing caching software such as nscd that uses the DNS TTL avoids most DNS lookups but makes the exact moment of change indeterminate.

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