Add an RPC fallback endpoint to the core services - #2524
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The cypress core services (reporter, vrf-core, request-response-core) read Kaia via a single BlockPI endpoint with no fallback, so when BlockPI's Cloudflare origin returns 520s (Aug 6 and Aug 24 incidents) block-number/contract reads fail across all three at once. The cypress node was unaffected because it reads public-en.node.kaia.io, not BlockPI. Wire the long-dead FALLBACK_PROVIDER_URL env into the read provider via a FallbackJsonRpcProvider that transparently retries a failed READ on the secondary endpoint. It avoids ethers' FallbackProvider (whose detectNetwork Promise.all over all backends lets a fallback-down-at-boot brick a healthy primary, and which enforces cross-endpoint block consensus). Here the fallback is touched only after the primary errors on a transient code; both endpoints carry RPC_URL_TIMEOUT so a hung primary fails over in seconds; eth_chainId and eth_sendRawTransaction never fail over; failover is logged (throttled). The listener reuses the shared PROVIDER singleton. Inert until FALLBACK_PROVIDER_URL is set (unset everywhere today = plain JsonRpcProvider, no behavior change). Tx submission uses caver, unaffected. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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📝 WalkthroughWalkthroughThe shared RPC provider now supports failover from a primary endpoint to a secondary endpoint for transient read errors. Chain ID and raw transaction calls do not fail over. Listener state uses the shared provider. ChangesRPC provider failover
Estimated code review effort: 3 (Moderate) | ~20 minutes Merge Risk: 🟡 Moderate · up to If the fallback endpoint is configured for the wrong network, ordinary reads or logs could cause listeners to process unrelated chain data. Merge should wait for chain-identity validation or explicit owner acceptance of this bounded configuration risk. Sequence Diagram(s)sequenceDiagram
participant Caller
participant FallbackJsonRpcProvider
participant PrimaryProvider
participant SecondaryProvider
Caller->>FallbackJsonRpcProvider: Send RPC request
FallbackJsonRpcProvider->>PrimaryProvider: Execute request
PrimaryProvider-->>FallbackJsonRpcProvider: Return transient error
FallbackJsonRpcProvider->>SecondaryProvider: Retry request
SecondaryProvider-->>FallbackJsonRpcProvider: Return response
FallbackJsonRpcProvider-->>Caller: Return response
Suggested reviewers: Poem
🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
Full details: Description checkExplanation The description provides a detailed summary, motivation, implementation context, safety considerations, tests, rollout plan, and known limitation. It does not include the template's issue reference, selected change type, checklist confirmations, or deployment selections, but the core information is complete. ✨ Finishing Touches 💡 1📝 Generate docstrings 💡
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Inline comments:
In `@core/src/settings.ts`:
- Around line 213-237: Update the failover provider around the custom provider’s
send method to cache the primary chain ID and verify the fallback provider
reports the same chain ID before returning fallback responses; reject
mismatched-chain fallbacks while leaving fallback probing lazy so startup does
not require its availability. Add an integration test using distinct primary and
fallback chain IDs and assert the request rejects.
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core/src/listener/state.tscore/src/settings.tscore/test/settings.test.ts
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Address review: if FALLBACK_PROVIDER_URL is misconfigured to another network, a primary outage could feed listeners foreign blocks/logs. Verify the fallback's chain ID matches the primary's before using it — lazily on the first failover (never at startup) and cached, so fallback availability is not a startup requirement. On mismatch the request rejects; on an unverifiable check the fallback is skipped and re-checked next time. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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Addressed the different-chain concern in the latest commit: |
🧩 Analysis chain🏁 Script executed: #!/bin/bash
set -euo pipefail
echo '=== Changed files ==='
git diff --name-status "$(git merge-base HEAD origin/main)" HEAD 2>/dev/null || git diff --name-status HEAD~1 HEAD
echo '=== Settings outline ==='
ast-grep outline core/src/settings.ts --items all --view expanded
echo '=== Provider-related settings source ==='
rg -n -C 10 'FallbackJsonRpcProvider|shouldFailoverRpc|createJsonRpcProvider|FALLBACK_PROVIDER_URL|PROVIDER\b' core/src/settings.ts
echo '=== Focused tests ==='
cat -n core/test/settings.test.ts
echo '=== Listener change context ==='
rg -n -C 8 'PROVIDER|JsonRpcProvider|provider' core/src/listener/state.ts
echo '=== PR diff for reviewed files ==='
git diff "$(git merge-base HEAD origin/main)" HEAD -- core/src/settings.ts core/test/settings.test.ts core/src/listener/state.ts 2>/dev/null \
|| git diff HEAD~1 HEAD -- core/src/settings.ts core/test/settings.test.ts core/src/listener/state.tsLength of output: 18977
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1 participant
Problem
The cypress core services (
reporter,vrf-core,request-response-core) read Kaia through a single BlockPI endpoint with no fallback. When BlockPI's Cloudflare origin returns 520s (2026-08-06 and 2026-08-24 daily reports), block-number/contract reads fail across all three at once — while the cypress node rode it out because it readspublic-en.node.kaia.io, not BlockPI.Fix
Wire the long-dead
FALLBACK_PROVIDER_URLenv (defined 2023, never used) into the read provider via a smallFallbackJsonRpcProviderthat transparently retries a failed read on the secondary endpoint.Deliberately not ethers'
FallbackProvider, which (a) doesPromise.allover all backends indetectNetwork— a fallback down at boot bricks a healthy primary — and (b) enforces cross-endpoint block consensus so a lagging fallback still errors. This provider touches the fallback only after the primary errors on a transient code (SERVER_ERROR/NETWORK_ERROR/TIMEOUT):RPC_URL_TIMEOUT(3s) so a hung-but-connected primary fails over in seconds vs ethers' ~2-min default;eth_chainIdandeth_sendRawTransactionnever fail over (no wrong-chain lock; no double-broadcast);Listener now reuses the shared
PROVIDERsingleton instead of a per-Stateprovider.Safety / rollout
Inert until enabled.
FALLBACK_PROVIDER_URLunset (everywhere today) → plainJsonRpcProvider, zero behavior change. Enable per network in Helm (public-en.node.kaia.iofor cypress,public-en-kairos.node.kaia.iofor baobab), baobab first. Tx submission untouched (caver).Tests
test/settings.test.tscovers the failover decision contract.tscclean, prettier clean. Reviewed twice adversarially — the redesign off ethers'FallbackProviderand the timeout /eth_chainId/ logging refinements came from that.(pre-commit hook bypassed locally: it runs jest over changed files which pulls in tests needing a local RPC at 127.0.0.1:8545; those fail on any machine without a node, unrelated to this change. CI runs the full suite.)
Known limitation
eth_getLogsfailover to a fallback lagging the primary's height errors (out-of-range) and the listener retries — best-effort, not seamless, for log-range reads.