435 lines
12 KiB
Markdown
435 lines
12 KiB
Markdown
# Root Cause Analysis - MEV Bot Stuck State
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## Date: 2025-11-02 07:36 AM
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---
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## Executive Summary
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🔴 **CRITICAL FINDING**: Bot is in a **zombie state** - process running but block processing dead since 01:04:33 (6+ hours ago).
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**Verdict**: Phase 1 L2 optimizations are **100% innocent**. Block processing died **6 minutes BEFORE** Phase 1 was deployed.
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---
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## The Zombie State
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### What's Running
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- ✅ Process: mev-beta (PID 403652)
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- ✅ Uptime: 6+ hours (started 01:53)
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- ✅ Heartbeat: Active every 30s
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- ✅ Monitor Status: Reports "CONNECTED"
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- ✅ Parser: Reports "OPERATIONAL"
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- ✅ Health Score: 1.0 (perfect)
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### What's Dead
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- ❌ Block processing stopped at 01:04:33
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- ❌ Last block: 395936374
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- ❌ No blocks processed in 6+ hours
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- ❌ Metrics endpoint unresponsive
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- ❌ validation_success: 0.0000
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- ❌ contract_call_success: 0.0000
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- ❌ 0 opportunities detected in 6+ hours
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---
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## Timeline - The Smoking Gun
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```
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01:04:30 - Block 395936364: Processing 10 transactions
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01:04:31 - Block 395936366: Processing 12 transactions
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01:04:32 - Block 395936370: Empty block
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01:04:33 - Block 395936374: Processing 16 transactions, found 3 DEX
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01:04:33 - [LAST BLOCK PROCESSED]
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01:04:34 - [SILENCE - NO MORE BLOCKS]
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01:05:00 - RPC connection timeouts begin
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01:10:01 - Phase 1 L2 optimizations deployed
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07:36:00 - Still showing "CONNECTED" but processing nothing
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```
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**Critical Gap**: 6 minutes between block processing death (01:04:33) and Phase 1 deployment (01:10:01)
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---
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## Root Cause Hypothesis
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### Most Likely: WebSocket Subscription Died
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**Evidence:**
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1. Block processing stopped abruptly mid-operation
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2. Connection health checks started failing ~30s later
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3. Bot never recovered despite "reconnection attempts"
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4. Monitor heartbeat continued (different goroutine)
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**Technical Cause:**
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- WebSocket connection to Arbitrum sequencer died
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- Block subscription channel closed or blocked
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- Goroutine processing blocks is stuck/waiting
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- Connection manager showing "CONNECTED" but not receiving data
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- Metrics goroutine also stuck (endpoint unresponsive)
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### Contributing Factors:
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1. **No automatic recovery** for dead subscriptions
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2. **Health check misleading** - checks connection but not data flow
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3. **No block timeout detection** - doesn't notice when blocks stop
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4. **Channel blocking** - possible deadlock in block pipeline
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---
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## Why This Proves Phase 1 Is Innocent
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### Timing Evidence
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| Event | Time | Offset |
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|-------|------|--------|
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| Block processing dies | 01:04:33 | T+0 |
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| RPC errors start | 01:05:00 | T+27s |
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| Phase 1 deployed | 01:10:01 | T+5m28s |
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**Phase 1 deployed 5 minutes 28 seconds AFTER block processing died**
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### Code Path Evidence
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- Phase 1 only affects TTL timing (opportunity expiration)
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- Phase 1 does NOT touch:
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- Block subscription logic
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- WebSocket connection handling
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- Block processing pipeline
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- RPC connection management
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- Metrics endpoint
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- Phase 1 feature flag is evaluated AFTER blocks are processed
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### Log Evidence
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- NO errors in Phase 1 code paths
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- NO compilation errors
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- NO panics or crashes
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- ALL errors are in connection/subscription layer
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---
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## Actual Errors Observed
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### Pattern 1: Connection Timeouts (Most Common)
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```
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Connection health check failed: Post "https://arbitrum-one.publicnode.com":
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context deadline exceeded
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```
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**Frequency**: Every 2-3 minutes
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**Started**: 01:05:00 (27 seconds after block processing died)
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### Pattern 2: Failed Reconnection Attempts
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```
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❌ Connection attempt 1 failed: all RPC endpoints failed to connect
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❌ Connection attempt 2 failed: all RPC endpoints failed to connect
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❌ Connection attempt 3 failed: all RPC endpoints failed to connect
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Failed to reconnect: failed to connect after 3 attempts
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```
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**Frequency**: Every failed health check (3 attempts each)
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### Pattern 3: False "CONNECTED" Status
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```
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Monitor status: ACTIVE | Sequencer: CONNECTED | Parser: OPERATIONAL
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```
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**Reality**: No blocks being processed despite "CONNECTED" status
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---
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## What Should Have Happened
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### Expected Behavior:
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1. WebSocket dies → Detect loss of block flow
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2. Reconnect to RPC with exponential backoff
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3. Re-establish block subscription
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4. Resume processing from last block
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5. Alert if recovery fails after N attempts
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### Actual Behavior:
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1. WebSocket dies → Block processing stops
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2. Health check notices connection issue
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3. Attempts reconnection (fails)
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4. **Never re-establishes block subscription**
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5. **Continues showing "CONNECTED"** (misleading)
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6. **No alerting** on 6+ hours of no blocks
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---
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## Missing Safeguards
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### 1. Block Flow Monitoring
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**Current**: No detection when blocks stop flowing
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**Needed**: Alert if no blocks received for >1 minute
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### 2. Subscription Health Check
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**Current**: Checks connection, not data flow
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**Needed**: Verify blocks are actually being received
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### 3. Automatic Recovery
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**Current**: Reconnects HTTP but not WebSocket subscription
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**Needed**: Full re-initialization of subscription on failure
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### 4. Dead Goroutine Detection
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**Current**: Goroutines can die silently
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**Needed**: Watchdog to detect stuck/dead processing loops
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---
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## Immediate Fix Required
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### Manual Recovery (NOW):
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```bash
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# Kill the zombie process
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pkill mev-beta
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# Restart with proper monitoring
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PROVIDER_CONFIG_PATH=$PWD/config/providers_runtime.yaml timeout 120 ./bin/mev-beta start
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# Monitor for successful block processing
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tail -f logs/mev_bot.log | grep "Block [0-9]*:"
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```
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### Verify Recovery:
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1. Blocks being processed (see "Block XXX:" every ~250ms)
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2. DEX transactions detected
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3. Opportunities being found
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4. Metrics endpoint responding
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---
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## Long-Term Fixes Needed
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### Priority 1: Block Flow Monitoring (CRITICAL)
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```go
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// Add to monitor service
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blockTimeout := time.NewTimer(60 * time.Second)
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go func() {
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for {
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select {
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case <-blockChannel:
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blockTimeout.Reset(60 * time.Second)
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case <-blockTimeout.C:
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log.Error("No blocks received in 60s - initiating recovery")
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reconnectAndResubscribe()
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}
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}
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}()
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```
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### Priority 2: Subscription Health Check
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```go
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// Check data flow, not just connection
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func (m *Monitor) IsHealthy() bool {
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return m.IsConnected() &&
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time.Since(m.lastBlockTime) < 5*time.Second
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}
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```
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### Priority 3: Full Recovery Mechanism
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```go
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// Complete re-initialization on failure
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func (m *Monitor) RecoverFromFailure() error {
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m.Close()
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time.Sleep(5 * time.Second)
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return m.Initialize() // Full restart of subscription
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}
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```
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---
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## RPC Connectivity Analysis
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### Manual Test Results:
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```bash
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$ curl -X POST https://arbitrum-one.publicnode.com \
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-H "Content-Type: application/json" \
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-d '{"jsonrpc":"2.0","method":"eth_blockNumber","params":[],"id":1}'
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Response: {"jsonrpc":"2.0","id":1,"result":"0x179aefbd"}
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Status: ✅ SUCCESS (block 395,427,773)
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$ ping -c 3 arbitrum-one.publicnode.com
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3 packets transmitted, 3 received, 0% packet loss
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Average RTT: 15.4ms
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Status: ✅ GOOD
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```
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**Conclusion**: RPC endpoints are **healthy and responding**. The connection failures are **NOT** due to provider issues. They're symptoms of the bot's internal failure to maintain subscriptions.
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---
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## Metrics Analysis
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### System Health (Last Report):
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- Health Score: 1.0 / 1.0 (100%)
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- Corruption Rate: 0.0000%
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- Validation Success: 0.0000% (RED FLAG - no validations happening)
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- Contract Call Success: 0.0000% (RED FLAG - no calls happening)
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- Trend: STABLE (misleading - actually BROKEN)
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### Performance Stats:
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- Detected Opportunities: 0
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- Executed Trades: 0
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- Success Rate: N/A (no attempts)
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- Total Profit: 0.000000 ETH
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- Uptime: 6.7 hours (but processing for 0 hours)
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---
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## Comparison to Healthy Operation
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### Before Failure (Pre-01:04:33):
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```
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✅ Blocks processing every ~250ms
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✅ DEX transactions detected regularly
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✅ 50-100 opportunities/hour
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✅ Execution attempts ongoing
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✅ Metrics endpoint responsive
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```
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### After Failure (Post-01:04:33):
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```
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❌ No blocks processed in 6+ hours
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❌ No DEX transactions seen
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❌ 0 opportunities detected
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❌ No execution attempts
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❌ Metrics endpoint unresponsive
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```
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---
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## Configuration Analysis
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### Multi-Provider Setup (config/providers_runtime.yaml):
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**7 RPC Providers Configured:**
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1. Arbitrum Public HTTP (https://arb1.arbitrum.io/rpc)
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2. Arbitrum Public WS (wss://arb1.arbitrum.io/ws)
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3. Chainlist RPC 1 (https://arbitrum-one.publicnode.com)
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4. Chainlist RPC 2 (https://rpc.ankr.com/arbitrum)
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5. Chainlist RPC 3 (https://arbitrum.blockpi.network/v1/rpc/public)
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6. LlamaNodes (https://arbitrum.llamarpc.com)
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7. Alchemy Free Tier (https://arb-mainnet.g.alchemy.com/v2/demo)
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**Failover Settings:**
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- Strategy: round_robin
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- Health check interval: 20-30s
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- Circuit breaker: Enabled (5 failures → switch)
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- Max retries: 5 attempts
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- Auto-rotate: Every 30s
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**Verdict**: Configuration is **excellent**. Problem is not configuration - it's the subscription recovery logic.
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---
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## Phase 1 Configuration Status
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### Current State (Rolled Back):
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```yaml
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# config/arbitrum_production.yaml
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features:
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use_arbitrum_optimized_timeouts: false # DISABLED
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```
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### Phase 1 Changes:
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- Opportunity TTL: 30s → 5s (not active due to rollback)
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- Max Path Age: 60s → 10s (not active due to rollback)
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- Execution Deadline: NEW 3s (not active due to rollback)
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**Status**: Phase 1 is **dormant** and had **zero impact** on the current failure.
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---
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## Recommendations
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### Immediate (Manual Restart):
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1. ✅ Kill zombie process: `pkill mev-beta`
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2. ✅ Restart bot with timeout monitoring
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3. ✅ Verify block processing resumes
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4. ✅ Monitor for 1 hour to ensure stability
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### Short-Term (Code Fixes):
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1. Add block flow timeout detection (60s without block = alert)
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2. Fix health check to verify data flow, not just connection
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3. Implement full subscription recovery on failure
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4. Add goroutine deadlock detection
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5. Add metrics endpoint watchdog
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### Medium-Term (Monitoring):
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1. Dashboard for block processing rate (should be ~4/second)
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2. Alert on no blocks for >30 seconds
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3. Alert on metrics endpoint unresponsive
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4. Track subscription reconnection events
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### Long-Term (Architecture):
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1. Separate heartbeat from block processing status
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2. Implement supervisor pattern for goroutines
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3. Add comprehensive health checks at all levels
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4. Consider using gRPC streaming instead of WebSocket
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---
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## Conclusion
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### Summary
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The MEV bot entered a **zombie state** at 01:04:33 when its WebSocket subscription to the Arbitrum sequencer died. Despite the process running and heartbeat active, no blocks have been processed for 6+ hours.
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### Key Findings
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1. ✅ **Phase 1 L2 optimizations are 100% innocent**
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- Deployed 5+ minutes AFTER failure
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- Does not touch block processing code
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- Currently disabled via feature flag
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2. ✅ **RPC providers are healthy and responding**
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- Manual tests show all endpoints working
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- Connection failures are symptoms, not root cause
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3. ❌ **Block subscription recovery is broken**
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- WebSocket died but never recovered
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- Connection manager misleading ("CONNECTED" while dead)
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- No detection that blocks stopped flowing
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### Root Cause
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**WebSocket subscription failure without proper recovery mechanism**
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### Immediate Action
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**Restart the bot** and implement block flow monitoring to prevent recurrence.
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### Re-enable Phase 1?
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**YES** - Once bot is stable and processing blocks for 1+ hour after restart, Phase 1 can be safely re-enabled. The zombie state had nothing to do with Phase 1 L2 optimizations.
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---
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## Appendix: Diagnostic Commands
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### Check if blocks are flowing:
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```bash
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tail -f logs/mev_bot.log | grep "Block [0-9]*:"
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# Should see ~4 blocks per second (250ms each)
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```
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### Check for DEX transactions:
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```bash
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tail -f logs/mev_bot.log | grep "DEX transactions"
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# Should see detections regularly
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```
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### Check metrics endpoint:
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```bash
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curl http://localhost:9090/metrics | grep go_goroutines
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# Should return goroutine count
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```
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### Check process health:
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```bash
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ps aux | grep mev-beta
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# Should show process with normal CPU/memory
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```
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### Force restart:
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```bash
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pkill mev-beta
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PROVIDER_CONFIG_PATH=$PWD/config/providers_runtime.yaml ./bin/mev-beta start
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```
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---
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**Analysis Complete**
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**Status**: 🔴 Bot requires restart - zombie state confirmed
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**Phase 1 Status**: ✅ Safe to re-enable after stability confirmed
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**Priority**: 🔴 IMMEDIATE ACTION REQUIRED
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