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Add client-side failover to CLI tool for redundancy testing

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All commands gain --failover-urls (-F) to specify alternate endpoints.
Short-lived commands try each URL in order on initial connect. The
subscribe command monitors KeepAlive and automatically reconnects to
the next available server, re-creating the subscription on failover.
Verified with live service start/stop: primary down triggers failover
to secondary, primary restart allows failback.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
This commit is contained in:
Joseph Doherty
2026-03-28 14:41:06 -04:00
parent a55153d7d5
commit afd6c33d9d
11 changed files with 334 additions and 28 deletions
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15
docs/Redundancy.md
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@@ -162,6 +162,21 @@ Application URI: urn:localhost:LmxOpcUa:instance1
The command also supports `--username`/`--password` and `--security` options for authenticated or encrypted connections.
### Client Failover with `-F`
All CLI commands support the `-F` / `--failover-urls` flag for automatic client-side failover. When provided, the CLI tries the primary endpoint first and falls back to the listed URLs if the primary is unreachable.
```bash
# Connect with failover — uses secondary if primary is down
dotnet run -- connect -u opc.tcp://localhost:4840/LmxOpcUa -F opc.tcp://localhost:4841/LmxOpcUa
# Subscribe with live failover — reconnects to secondary if primary drops mid-stream
dotnet run -- subscribe -u opc.tcp://localhost:4840/LmxOpcUa -F opc.tcp://localhost:4841/LmxOpcUa \
-n "ns=1;s=TestMachine_001.MachineID"
```
For long-running commands (`subscribe`), the CLI monitors the session KeepAlive and automatically reconnects to the next available server when the current session drops. The subscription is re-created on the new server.
## Troubleshooting
**Mismatched ServerUris between instances** -- Both instances must list the exact same set of ApplicationUri values in `Redundancy.ServerUris`. If they differ, clients may not discover the full redundant set. Check the startup log for the `Redundancy.ServerUris` line on each instance.