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V2_TO_V3_GUIDE.md

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Migrating from xDS v2 to v3

To faciliate migrating from the v2 xDS APIs to v3, this repo supports both the v2 and v3 gRPC transports, with each transport supporting type URL rewriting of DiscoveryResponse to whatever version the client requests with api_resource_version.

The migration requires care - for example, using v3-only fields too soon or trying to use deprecated v2 fields too late can cause Envoy to reject or improperly apply config.

Recommended Sequence

This section assumes you have sufficient control over Envoy sidecar versions that you do not need to run v2 and v3 simultaneously for a long migration period.

  1. Make sure your oldest Envoy client supports final v2 message versions.
    1. Ensure your control plane is not using any deprecated v2 fields. Deprecated v2 fields will cause errors when they are translated to v3 (because deprecated v2 fields are dropped in v3).
    2. Configure a V3DiscoveryServer alongside the V2DiscoveryServer in your control plane. You can (and should) use the same (v2) Cache implementation in both servers.
  3. Deploy all Envoy clients to switch to both the v3 transport_api_version and resource_api_version in each respective xDS configs. As this happens, the V3DiscoveryServer will be translating your v2 resources to v3 automatically, and the V2DiscoveryServer will stop being used.
    1. Rewrite your control plane code to use v3 resources, which means using V3SimpleCache (if you use SimpleCache). You may now start using v3-only message fields if you choose.
    2. Drop the V2DiscoveryServer.

Alternative

Another possible path to the one above is to switch to generating v3 in the control plane first (e.g. by using V3SimpleCache) and then deploying Envoy clients to use v3 transport and resource versions.

This approach requires care to not use new V3-only fields until the client side upgrade is complete (or at least understand the consequences of doing so).