Add jfr event for dns lookup

[NeatGuyCoding]

Necessity of Adding DNS Lookup JFR Event

Cloud-native environments rely heavily on DNS for service discovery, where DNS queries are frequent and latency-critical. Java's DNS caching policy (default 30s TTL) significantly impacts performance.

Problems:

• Cannot distinguish cache hits from actual queries
• DNS latency is difficult to track and diagnose
• Multiple libraries concurrently resolving domains cause redundant queries

Value:

• Complete traceability: DNS query → Socket connect → Data transfer
• Troubleshooting: Identify DNS timeouts, resolution failures
• Performance optimization: Evaluate cache policies, discover hotspot domains
• Security audit: Track external domains accessed

This event complements SocketRead/Write events, enhancing network observability.

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[mrserb]

It might be useful to differentiate between three use cases:

• Successful/Error requests when caches are disabled or not used -> these represent actual network DNS lookups
• Successful/Error requests returned from the cache -> the application may see many repeated errors not due to new DNS failures, but because a previous error response was cached
• Successful/Semi-Error requests -> this occurs when a DNS error happens, but the application continues to function because a stale cached record is used

It might also be useful to include some information about the DNS cache itself — for example, whether the result came from cache, the TTL of the entry, or whether stale data was used.
BTW, there is also a mechanism to clean up the cache; perhaps we could expose metrics such as the current cache size, number of entries removed, and number of stale entries.

What do you think?

[NeatGuyCoding]

It might be useful to differentiate between three use cases:

• Successful/Error requests when caches are disabled or not used -> these represent actual network DNS lookups
• Successful/Error requests returned from the cache -> the application may see many repeated errors not due to new DNS failures, but because a previous error response was cached
• Successful/Semi-Error requests -> this occurs when a DNS error happens, but the application continues to function because a stale cached record is used

It might also be useful to include some information about the DNS cache itself — for example, whether the result came from cache, the TTL of the entry, or whether stale data was used. BTW, there is also a mechanism to clean up the cache; perhaps we could expose metrics such as the current cache size, number of entries removed, and number of stale entries.

What do you think?

Thanks for the reply, I will investigate and make some updates

[NeatGuyCoding]

@mrserb redesigned, kindly check, thanks

[AlanBateman]

Please start a discussion on net-dev. Also keep in mind that these methods use whatever name service is configured so the lookups may not be DNS. This will influence the naming, if events are introduced.

[NeatGuyCoding]

email sent to [email protected]
Thanks @AlanBateman