Module org.elasticsearch.server
Package org.elasticsearch

Record Class TransportVersion

java.lang.Object
java.lang.Record
org.elasticsearch.TransportVersion
All Implemented Interfaces:
Comparable<TransportVersion>, VersionId<TransportVersion>
public record TransportVersion(int id) extends Record implements VersionId<TransportVersion>
Represents the version of the wire protocol used to communicate between a pair of ES nodes.

Prior to 8.8.0, the release Version was used everywhere. This class separates the wire protocol version from the release version.

Each transport version constant has an id number, which for versions prior to 8.9.0 is the same as the release version for backwards compatibility. In 8.9.0 this is changed to an incrementing number, disconnected from the release version.

Each version constant has a unique id string. This is not actually used in the binary protocol, but is there to ensure each protocol version is only added to the source file once. This string needs to be unique (normally a UUID, but can be any other unique nonempty string). If two concurrent PRs add the same transport version, the different unique ids cause a git conflict, ensuring that the second PR to be merged must be updated with the next free version first. Without the unique id string, git will happily merge the two versions together, resulting in the same transport version being used across multiple commits, causing problems when you try to upgrade between those two merged commits.

Version compatibility

The earliest compatible version is hardcoded in the MINIMUM_COMPATIBLE field. Previously, this was dynamically calculated from the major/minor versions of Version, but TransportVersion does not have separate major/minor version numbers. So the minimum compatible version is hard-coded as the transport version used by the highest minor release of the previous major version. MINIMUM_COMPATIBLE should be updated appropriately whenever a major release happens.

The earliest CCS compatible version is hardcoded at MINIMUM_CCS_VERSION, as the transport version used by the previous minor release. This should be updated appropriately whenever a minor release happens.

Scope of usefulness of TransportVersion

TransportVersion is a property of the transport connection between a pair of nodes, and should not be used as an indication of the version of any single node. The TransportVersion of a connection is negotiated between the nodes via some logic that is not totally trivial, and may change in future. Any other places that might make decisions based on this version effectively have to reproduce this negotiation logic, which would be fragile. If you need to make decisions based on the version of a single node, do so using a different version value. If you need to know whether the cluster as a whole speaks a new enough TransportVersion to understand a newly-added feature, use ClusterState.getMinTransportVersion().