infra: add watchdog for batcher (#1311)

infra/watchdog/batcher/.env.example

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+PROMETHEUS_URL=<ip>:<port>
+SYSTEMD_SERVICE=batcher
+PROMETHEUS_COUNTER=sent_batches
+PROMETHEUS_BOT=batcher
+PROMETHEUS_INTERVAL=20m
+SLACK_WEBHOOK_URL=<>

infra/watchdog/batcher/README.md

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+# Batcher Watchdog
+
+The Batcher Watchdog checks a prometheus metric and restart the Batcher as needed.
+
+The metric is the quantity of batches sent in the last N minutes, defined in the PROMETHEUS_INTERVAL variable. Lets call this metric `sent_batches`.
+
+Since we are sending proofs constantly, the ideal behaviour is the creation of a task every 3 Ethereum blocks (~36 secs). So, if the `sent_batches` metrics is 0 it means there is a problem in the Batcher, for example a transaction is stuck in Ethereum and the Batcher is locked waiting for the transaction. If this happens, the Watchdog restarts the Batcher.
+
+## Configuration
+
+You need to create a .env file with the following variables
+
+```
+PROMETHEUS_URL=<ip>:<port>
+SYSTEMD_SERVICE=batcher
+PROMETHEUS_COUNTER=sent_batches
+PROMETHEUS_BOT=batcher
+PROMETHEUS_INTERVAL=20m
+SLACK_WEBHOOK_URL=<>
+```
+
+There is a `.env.example` file in this directory.
+
+## Run with Crontab
+
+Open the Crontab configuration with `crontab -e` and add the following line:
+
+```
+*/10 * * * * /path/to/watchdog/batcher_watchdog.sh /path/to/config/.env >> /path/to/logs/folder/batcher_watchdog.log 2>&1
+```
+
+The cron interval has to be the half of PROMETHEUS_INTERVAL (PROMETHEUS_INTERVAL/2).
+
+You can check logs in the specified file, for example:
+
+```
+Tue Oct 15 08:00:01 UTC 2024: tasks created in the last 20m: "25"
+Tue Oct 15 08:20:01 UTC 2024: tasks created in the last 20m: "2"
+Tue Oct 15 08:40:01 UTC 2024: tasks created in the last 20m: "0"
+Tue Oct 15 08:40:01 UTC 2024: restarting batcher
+Tue Oct 15 08:40:01 UTC 2024: batcher restarted
+```

infra/watchdog/batcher/batcher_watchdog.sh

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+#!/bin/bash
+
+# Load env file from first parameter
+# Env variables:
+#   - PROMETHEUS_URL
+#   - SYSTEMD_SERVICE
+#   - PROMETHEUS_COUNTER
+#   - PROMETHEUS_BOT
+#   - PROMETHEUS_INTERVAL
+#   - SLACK_WEBHOOK_URL
+source $1
+
+# Function to send slack message
+# @param message
+function send_slack_message() {
+  curl -X POST -H 'Content-type: application/json' \
+    --data "{\"text\":\"$1\"}" \
+    $SLACK_WEBHOOK_URL
+}
+
+# Get rate from prometheus
+rate=$(curl -gs 'http://'$PROMETHEUS_URL'/api/v1/query?query=floor(increase('$PROMETHEUS_COUNTER'{bot="'$PROMETHEUS_BOT'"}['$PROMETHEUS_INTERVAL']))' | jq '.data.result[0].value[1]')
+
+echo "$(date): tasks created in the last $PROMETHEUS_INTERVAL: $rate"
+
+# Check if rate is 0
+if [ "$rate" = \"0\" ]; then
+  # Restart systemd service
+  echo "$(date): restarting $SYSTEMD_SERVICE"
+  sudo systemctl restart $SYSTEMD_SERVICE
+  message="$(date): $SYSTEMD_SERVICE restarted by watchdog"
+  echo $message
+  send_slack_message "$message"
+fi