keepalivetimeout

Keepalivetimeout is a configuration concept used in networking to specify how long a connection may remain idle before the system takes action to verify liveness or to close the connection. The exact meaning of the term can vary by context, but it generally governs the balance between keeping connections reusable and reclaiming resources.

In the TCP layer, keepalive timing is typically implemented as a set of host-level parameters rather than part of the core TCP protocol. A common model uses three values: the idle time before the first keepalive probe is sent, the interval between successive probes if there is no reply, and the maximum number of probes sent before the connection is considered dead. If the remote end does not respond to probes, the connection is closed. These values are exposed as system-level settings in many operating systems (for example, Linux provides tcp_keepalive_time, tcp_keepalive_intvl, and tcp_keepalive_probes; Windows exposes KeepAliveTime and KeepAliveInterval). Defaults vary by platform but are typically on the order of hours for the idle period, with shorter intervals between probes and a small probe count.

In HTTP servers and proxies, keep-alive timeout typically refers to how long a persistent connection can remain idle while awaiting the next request before the server closes it. This is distinct from TCP keepalive probes and is configured at the application layer. Examples include the keepalive_timeout directive in Nginx and the KeepAliveTimeout setting in Apache. These timeouts affect connection reuse, throughput, and resource consumption.

Keepalivetimeout also appears in other contexts, such as database clients or messaging systems, where it helps detect dead peers and reclaim connections or leases.

In practice, administrators choose values to balance low latency and resource usage, monitor connection churn, and adjust per environment and workload. See also keepalive and timeout concepts.