Motivation

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Because of that, some protocols implement keepalive logic on a higher level (SMB, TLS). More details: https://blog.stephencleary.com/2009/05/detection-of-half-open-dropped.html

Proposal

• Add OP_HEARTBEAT to the protocol with an empty payload. Clients can send heartbeats at a configurable interval and receive responses to ensure that the connection is active.
• Add OP_GET_IDLE_TIMEOUT to the protocol that returns server-side idle timeout (see ClientConnectorConfiguration.idleTimeout) as int64 milliseconds. When server.heartbeatInterval is less than client.idleTimeout, log a warning on the client.
• Add ClientConfiguration.heartbeatInterval property. Defaults to 0 (heartbeats disabled).

As a result:

• Client can identify a broken connection by sending OP_HEARTBEAT to the server.
• Server can identify a broken connection with the existing idleTimeout functionality.

This applies to Ignite 2.x and 3.x.

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• New ProtocolBitmaskFeature will be added to maintain protocol compatibility.TODO: Should we set heartbeat interval automatically according to ClientConnectorConfiguration#idleTimeout?
• When client-side heartbeats are enabled (not by default), server will no longer disconnect an otherwise idle client. This should be carefully documented and cross-linked.

Discussion Links

• Dev list
• IGNITE-16462 .NET: Thin client: add heartbeats · Pull Request #9817

Reference Links

• Wikipedia: TCP Half-open
• RFC 6520 TLS Heartbeat
• Detection of Half-Open (Dropped) Connections

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