Support bookie server config tcp keep-alive

[wolfstudy]

Motivation

In PR #4683, we introduced support for configuring TCP keep-alive parameters (TCP_KEEPIDLE, TCP_KEEPINTVL, TCP_KEEPCNT) on the Bookie client side (PerChannelBookieClient). This allowed users to fine-tune keep-alive behavior per connection instead of relying solely on the kernel-level defaults defined in /proc/sys/net/ipv4/tcp_keepalive_*.

However, as discussed in apache/pulsar#25580, a one-sided configuration is not enough. TCP keep-alive is a per-socket setting that works independently on each end of a connection. If only the client enables custom keep-alive parameters while the server still uses the OS-level defaults, operators are still forced to tune the kernel parameters of the host on which the Bookie runs in order to achieve a consistent end-to-end keep-alive behavior. This defeats the purpose of having fine-grained, application-level control and makes it cumbersome to deploy Bookies in environments where modifying OS-wide TCP settings is not permitted (e.g., shared or managed hosts).

To close this gap, we need to provide the same configurability on the Bookie server side (BookieNettyServer), so that a complete, symmetric TCP keep-alive configuration can be achieved from BookKeeper itself, without requiring any changes to the underlying operating system.

Changes

• ServerConfiguration: added serverTcpKeepIdle / serverTcpKeepIntvl / serverTcpKeepCnt, all defaulting to -1 (meaning "use OS default").
• BookieNettyServer: applies the new options via EpollChannelOption.TCP_KEEPIDLE / TCP_KEEPINTVL / TCP_KEEPCNT when the event loop is EpollEventLoopGroup, and only when the value is > 0. For Nio / IoUring / Default event loops, behavior falls back to the original SO_KEEPALIVE — fully backward compatible.

Backward Compatibility

All new options default to -1 and Epoll-specific channel options are only applied on EpollEventLoopGroup. Existing deployments see no behavior change after upgrading.

References

• Client-side support: Supports configuring TCP Keepalive related parameters in Bookie Client. #4683
• Motivation for symmetric server+client config: [feat][broker]:Support broker configuration for BookKeeper client TCP keep-alive options pulsar#25580

[wenbingshen]

LGTM

[wolfstudy]

@lhotari @wenbingshen PTAL again, thanks

[lhotari]

LGTM

[wolfstudy]

rerun failure checks