Enhance validator reliability with fallback beacon nodes

To configure a validator using Prysm with fallback beacon nodes, you can leverage Prysm's built-in support for multiple beacon node endpoints. The fallback provides load balancing and redundancy—if one beacon node becomes unresponsive, the validator client will automatically fall back to the others. The configuration uses the --beacon-rpc-provider with comma-separated gRPC endpoints (e.g., host:port pairs) or the --beacon-rest-api-provider flag with with comma-separated HTTP URLs (e.g., http://localhost:3500,http://remote:3500).

Prerequisites

• Ensure you have Prysm installed (e.g., via binaries from the official releases or built from source).
• Set up at least two beacon nodes (local or remote) that your validator can connect to. Each beacon node should be running and exposing its gRPC port (default: 4000).
• Generate or import your validator keys and wallet (e.g., using prysm validator wallet create).

Step-by-Step Configuration

1. Run the Validator Client with Fallback Endpoints:

   gRPC (default): Use --beacon-rpc-provider with comma-separated host:port pairs (gRPC port, default: 4000):

   ./prysm.sh validator \
     --wallet-dir=/path/to/wallet \
     --beacon-rpc-provider=localhost:4000,remote-beacon.example.com:4000,another-beacon:4000 \
     --datadir=/path/to/validator/data \
     --mainnet \
     --suggested-fee-recipient=0xYourEthereumAddressForFees

   REST: Use --beacon-rest-api-provider with comma-separated HTTP URLs (REST port, default: 3500). Each beacon node must also be started with --enable-beacon-rest-api:

   ./prysm.sh validator \
     --wallet-dir=/path/to/wallet \
     --beacon-rest-api-provider=http://localhost:3500,http://remote-beacon.example.com:3500,http://another-beacon:3500 \
     --datadir=/path/to/validator/data \
     --mainnet \
     --suggested-fee-recipient=0xYourEthereumAddressForFees

   Other common flags:

   • --graffiti="YourCustomGraffiti": Optional, for custom block graffiti.
   • --wallet-password-file=/path/to/password.txt: For non-interactive runs.
   • --enable-doppelganger: Enables doppelganger protection but may interfere with fallbacks in some cases (e.g., if the primary node is down during startup—test this in a dev environment).

Fallback behavior

Both gRPC and REST use the same sync-status-aware failover logic: the validator checks that each candidate node is both reachable and fully synced before accepting it. If the current endpoint becomes unhealthy or unsynced, the validator tries each remaining host once in order and stops at the first healthy one. When a switch occurs, it logs Failover succeeded with the previousHost, newHost, and failedAttempts fields.

2. Incorporate Health Checks (Including maxHealthChecks from PR #15401):

   • In the OffchainLabs/prysm fork, Pull Request #15401 introduces enhancements for safe validator shutdowns and restarts based on health checks of the connected beacon nodes. This health check is instrumental in fallback setups, handling scenarios where all beacon nodes become unhealthy.
   • (Optional) The key addition is the --max-health-checks flag, which controls the maximum number of consecutive failed health checks before the validator client times out and shuts down gracefully (allowing for restarts or manual intervention).
     • Usage: Add it to your validator command, e.g.:

       ./prysm.sh validator \
         --wallet-dir=/path/to/wallet \
         --beacon-rpc-provider=localhost:4000,remote-beacon.example.com:4000 \
         --max-health-checks=10 \
         --datadir=/path/to/validator/data \
         --mainnet
     • Explanation of maxHealthChecks:
       • Value: An integer specifying the max failed checks (e.g., 10). The validator will log warnings, such as "Failed health check, beacon node is unresponsive (fails=X maxFails=Y)" during issues.
       • Special value: 0 for indefinite checks (no timeout, keeps retrying forever).
       • Default: Not specified in the PR (check your build's flags with --help), but typically finite to prevent indefinite hangs.
       • This flag works alongside fallbacks: If all endpoints fail health checks (e.g., syncing issues or connectivity loss), the counter increments until reaching the limit, triggering a shutdown. Its design is to improve reliability in multi-node setups, with compatibility for gRPC load balancing and multiple beacon node HTTP resolvers.

3. Monitoring and Testing:

   • Monitor logs for health check messages or fallback switches. When the validator switches endpoints, it logs Failover succeeded with previousHost, newHost, and failedAttempts fields. Debug-level logs (e.g., Node is not ready) are emitted during health checks.
   • Use tools like Prometheus and Grafana (enabled via --monitoring-port=8081) to track validator performance.
   • Test fallbacks: Shut down one beacon node and verify the validator continues attesting/proposing via the others.
   • If enabling features like MEV-Boost, add --http-mev-relay=http://mev-relay.example.com for external builders, with automatic fallback to local execution if needed.

Potential Issues and Tips

• Doppelganger Protection: If enabled, it might prevent quick fallbacks during startup if the primary node is down. Disable it temporarily for testing.
• Network-Specific Flags: Use --mainnet, --holesky, or --sepolia depending on your chain.
• Security: Expose gRPC/HTTP ports securely (e.g., via TLS with --tls-cert and --tls-key).
• For advanced setups (e.g., Kubernetes), use environment variables like BEACON_RPC_PROVIDER instead of flags.

This setup ensures high availability for your validator. If you encounter errors, join the Prysm Discord community for support.