Cross-Cluster Replication

What it shows

Active-active cross-cluster replication. This sample stands up two independent in-process Orleans clusters (site-a and site-b), wires them together with Orleans.Lattice replication over the canonical gRPC push transport, then writes a key on site-a only and watches it converge onto site-b - with no direct write to site-b. The orders tree is opted into replication as a last-writer-wins register; each site ships its mutations to the other.

Like the CrossClusterAuthorization sample, it hosts both clusters in one process, each on its own ASP.NET Core / Kestrel pipeline, because the gRPC replication receiver is served over HTTP/2 (here plaintext h2c on loopback).

Run it

dotnet run --project samples/CrossClusterReplication

Expected output

Starting two independent Orleans clusters (site-a, site-b)...
Both clusters ready and peered over gRPC.

== Before ==
  site-b sees 'order/1001' = (absent)

== Writing on site-a only ==
  site-a wrote 'order/1001' = CONFIRMED

== Waiting for convergence on site-b (no direct write) ==
  .  converged.
  site-b now sees 'order/1001' = CONFIRMED

[OK] the write made on site-a converged onto site-b across clusters.

(The number of . poll dots before convergence varies run to run with shipping latency; the before/after values and the converged result are stable.)

When to use

Multi-region / multi-datacenter deployments that want each region to serve reads and writes locally while staying eventually consistent with the others.
Active-active topologies where any cluster may write any replicated tree and conflicting updates must converge deterministically by CRDT merge mode.

When not to use

Single-cluster deployments - replication adds a shipping pipeline you do not need. Use plain AddLattice there.
Strong/linearizable cross-region consistency. Replication is convergent and causally consistent, not a global consensus protocol.

Notes on this sample

Uses plaintext HTTP/2 (h2c) on loopback with AllowPlaintextEndpoints = true. Each site binds Kestrel to HTTP/2 with no certificate and grpc-dotnet speaks h2c by prior knowledge over an http:// address, so no process-wide switch is involved. Production deployments should use https:// peer endpoints and leave AllowPlaintextEndpoints at its secure default.
Receiver-side shared-secret authentication is turned off (RequireAuthentication = false) because this is a loopback demo with no secret material. Production must supply a secret and leave authentication on.
The gRPC ports default to 17001 / 17002, and the two clusters also bind Orleans silo ports 11111 / 11112 and gateway ports 30000 / 30001; change them in Program.cs if those are taken on your machine.

Feature docs

docs/lattice.replication/README.md

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