Honor networkaddress.cache.ttl to allow DNS refreshes
#12
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Currently, FHttp uses a permanent cache of DNS lookups, which causes problems when applications are pointed at DNS entries whose values are subject to change (for example, AWS Elastic Load Balancers).
This issue has affected Finagle generally, as discussed here. A fix went into Finagle last year. However, the
hosts()method ofClientBuilder, which is used by FHttp, does not take advantage of the fix.With the change in this Pull Request, FHttp will use a Finagle resolver that refreshes DNS entries on a timer if the Java Security property
networkaddress.cache.ttlis set to a positive value. If that property is negative or unset, FHttp will behave as it currently does.