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When a security manager is present, the JVM will cache positive hostname lookups indefinitely. This can be problematic, especially in the modern world with cloud services where DNS addresses can change, or environments using Docker containers where IP addresses could be considered ephemeral. This behavior impacts cluster discovery, cross-cluster replication and cross-cluster search, reindex from remote, snapshot repositories, webhooks in Watcher, external authentication mechanisms, and the Elastic Stack Monitoring Service. The experience of watching a DNS lookup change yet not be reflected within Elasticsearch is a poor experience for users. The reason the JVM has this is guard against DNS cache posioning attacks. Yet, there is already a defense in the modern world against such attacks: TLS. With proper certificate validation, even if a resolver falls prey to a DNS cache poisoning attack, using TLS would neuter the attack. Therefore we have a policy with dubious security value that significantly impacts usability. As such we make the usability/security tradeoff towards usability, since the security risks are very low. This commit introduces new system properties that Elasticsearch observes to override the JVM DNS cache policy.
20 lines
1.2 KiB
Plaintext
20 lines
1.2 KiB
Plaintext
[[networkaddress-cache-ttl]]
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=== DNS cache settings
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Elasticsearch runs with a security manager in place. With a security manager in
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place, the JVM defaults to caching positive hostname resolutions indefinitely
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and defaults to caching negative hostname resolutions for ten
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seconds. Elasticsearch overrides this behavior with default values to cache
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positive lookups for sixty seconds, and to cache negative lookups for ten
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seconds. These values should be suitable for most environments, including
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environments where DNS resolutions vary with time. If not, you can edit the
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values `es.networkaddress.cache.ttl` and `es.networkaddress.cache.negative.ttl`
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in the <<jvm-options,JVM options>>. Note that the values
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http://docs.oracle.com/javase/8/docs/technotes/guides/net/properties.html[`networkaddress.cache.ttl=<timeout>`]
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and
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http://docs.oracle.com/javase/8/docs/technotes/guides/net/properties.html[`networkaddress.cache.negative.ttl=<timeout>`]
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in the
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http://docs.oracle.com/javase/8/docs/technotes/guides/security/PolicyFiles.html[Java
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security policy] are ignored by Elasticsearch unless you remove the settings for
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`es.networkaddress.cache.ttl` and `es.networkaddress.cache.negative.ttl`.
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