Storage Backup and Recovery

Introduction

Data durability is a critical aspect of any monitoring system. While Prometheus is primarily designed for real-time monitoring rather than long-term data storage, there are scenarios where preserving historical metrics becomes essential - whether for compliance, capacity planning, or post-incident analysis.

This guide explores the strategies and techniques for backing up and recovering Prometheus data, helping you implement robust data protection practices in your monitoring infrastructure.

Understanding Prometheus Storage

Before diving into backup strategies, let's understand how Prometheus stores data:

Prometheus uses a custom time-series database called TSDB (Time Series Database) that stores metrics data on disk. By default, this data is stored in the /data directory, which contains:

• The actual time-series data organized in 2-hour blocks
• Write-ahead logs (WAL) that protect against data loss during crashes
• Various index files for efficient querying

The standard retention period is 15 days, but this can be configured using the --storage.tsdb.retention.time flag.

Why Back Up Prometheus Data?

While Prometheus is designed with a focus on operational monitoring rather than long-term storage, there are several reasons to implement a backup strategy:

1. Disaster Recovery: Protect against hardware failures, accidental deletions, or corruption
2. Historical Analysis: Preserve important metrics for long-term trend analysis
3. Compliance Requirements: Meet regulatory requirements for data retention
4. Migration: Facilitate smooth transitions between Prometheus instances

Backup Strategies

1. Snapshot-based Backups

Prometheus provides a built-in HTTP API endpoint that triggers a snapshot of the current data storage:

bash

# Create a snapshot of Prometheus data
curl -XPOST http://prometheus-server:9090/api/v1/admin/tsdb/snapshot

This creates a snapshot in the data/snapshots directory with minimal disruption to the running Prometheus instance.

You can then copy this snapshot to a secure location:

bash

# Copy the latest snapshot to backup location
cp -r /path/to/prometheus/data/snapshots/<snapshot-id> /backup/location/

2. File System Backup

For a more traditional approach, you can use standard file system backup tools to copy the Prometheus data directory. However, this method requires careful handling:

bash

# First, create a consistent backup using the HTTP API
curl -XPOST http://prometheus-server:9090/api/v1/admin/tsdb/snapshot

# Then use rsync to copy the snapshot to backup location
rsync -av /path/to/prometheus/data/snapshots/<snapshot-id>/ /backup/location/

caution

Never directly copy the active Prometheus data directory without using snapshots, as this can lead to inconsistent backups due to ongoing writes.

3. Remote Storage Integration

Prometheus can be configured to send a copy of all samples to a remote storage system, which serves as both a backup and a solution for long-term storage:

yaml

# prometheus.yml
remote_write:
  - url: "http://remote-storage-server/write"
    
remote_read:
  - url: "http://remote-storage-server/read"

Popular remote storage options include:

• Thanos
• Cortex
• M3DB
• VictoriaMetrics
• Prometheus itself (federated setup)

Let's visualize the remote storage workflow:

Recovery Procedures

Recovering from Snapshots

To recover Prometheus data from a snapshot:

1. Stop the Prometheus service:

   bash

   systemctl stop prometheus

2. Move the current data directory to a backup location:

   bash

   mv /path/to/prometheus/data /path/to/prometheus/data.bak

3. Create a new data directory:

   bash

   mkdir -p /path/to/prometheus/data

4. Copy the snapshot data to the new data directory:

   bash

   cp -r /backup/location/<snapshot-id>/* /path/to/prometheus/data/

5. Set appropriate permissions:

   bash

   chown -R prometheus:prometheus /path/to/prometheus/data

6. Restart Prometheus:

   bash

   systemctl start prometheus

Recovering from Remote Storage

If you've been writing to remote storage, you can recover by:

1. Configure a new Prometheus instance to read from the remote storage
2. Use the --storage.tsdb.retention.time flag to control how much local data to keep
3. Start backfilling data as needed using remote_read

Best Practices

1. Automate Backups: Schedule regular snapshots and offsite transfers

   bash

   # Example cron job for daily snapshots
   0 2 * * * curl -XPOST http://prometheus-server:9090/api/v1/admin/tsdb/snapshot && rsync -av /path/to/prometheus/data/snapshots/$(ls -t /path/to/prometheus/data/snapshots/ | head -n1) /backup/location/

2. Test Recovery Procedures: Regularly verify that backups can be successfully restored

3. Implement Monitoring for Backups: Monitor the backup process itself with Prometheus

   yaml

   # Example alert rule
   - alert: PrometheusBackupMissing
     expr: time() - prometheus_backup_last_successful_time_seconds > 86400
     for: 1h
     labels:
       severity: warning
     annotations:
       summary: "Prometheus backup missing"
       description: "No successful Prometheus backup in the last 24 hours"

4. Document Recovery Procedures: Ensure all team members understand how to perform recovery

5. Use Version Control for Configuration: Keep your Prometheus configuration files in version control

Implementing a Complete Backup Solution

Let's create a simple shell script that handles the snapshot creation and backup process:

bash

#!/bin/bash
# prometheus-backup.sh

# Configuration
PROMETHEUS_URL="http://localhost:9090"
BACKUP_DIR="/backup/prometheus"
RETENTION_DAYS=30

# Create timestamp
TIMESTAMP=$(date +%Y%m%d-%H%M%S)

# Create snapshot
echo "Creating Prometheus snapshot..."
SNAPSHOT_ID=$(curl -s -XPOST ${PROMETHEUS_URL}/api/v1/admin/tsdb/snapshot | jq -r '.data.name')

if [ -z "$SNAPSHOT_ID" ]; then
  echo "Failed to create snapshot!"
  exit 1
fi

echo "Created snapshot: $SNAPSHOT_ID"

# Wait for snapshot to complete
sleep 5

# Copy snapshot to backup location
SNAPSHOT_PATH="/var/lib/prometheus/data/snapshots/$SNAPSHOT_ID"
BACKUP_PATH="$BACKUP_DIR/$TIMESTAMP"

echo "Copying snapshot to $BACKUP_PATH..."
mkdir -p $BACKUP_PATH
cp -r $SNAPSHOT_PATH/* $BACKUP_PATH/

# Set appropriate permissions
chmod -R 755 $BACKUP_PATH

# Clean up old backups
find $BACKUP_DIR -type d -mtime +$RETENTION_DAYS -exec rm -rf {} \; 2>/dev/null || true

echo "Backup completed successfully!"

Using Thanos for Long-term Storage

For more advanced setups, Thanos offers a comprehensive solution for long-term storage and high availability:

yaml

# prometheus.yml with Thanos sidecar
global:
  external_labels:
    monitor: 'prometheus-server'

storage:
  tsdb:
    path: /data
    retention.time: 15d
  
# No changes needed to scrape configs

The Thanos sidecar can be run alongside Prometheus:

bash

thanos sidecar \
  --tsdb.path /data \
  --prometheus.url http://localhost:9090 \
  --objstore.config-file bucket.yml

Where bucket.yml contains the object storage configuration:

yaml

type: S3
config:
  bucket: "prometheus-backups"
  endpoint: "s3.amazonaws.com"
  access_key: "ACCESS_KEY"
  secret_key: "SECRET_KEY"
  insecure: false

Summary

Implementing a robust backup and recovery strategy for Prometheus is essential for ensuring data durability and system reliability. In this guide, we've covered:

• Understanding Prometheus's storage architecture
• Different backup strategies including snapshots and remote storage
• Step-by-step recovery procedures
• Best practices for managing backups
• Advanced solutions using Thanos

Remember that while Prometheus itself is designed for operational monitoring rather than long-term storage, these backup strategies can help you preserve critical metrics data for compliance, analysis, and disaster recovery purposes.

Additional Resources

• Prometheus Storage Documentation
• Thanos Project for distributed Prometheus with long-term storage
• Cortex Project for horizontally scalable Prometheus
• VictoriaMetrics for long-term storage and high performance

Exercises

1. Set up a daily snapshot backup for your Prometheus instance and verify that snapshots are being created correctly.
2. Create a recovery plan for your Prometheus deployment and practice restoring from a backup.
3. Configure Prometheus with remote write to a secondary Prometheus instance and test the failover process.
4. Experiment with Thanos to implement a long-term storage solution for your metrics data.
5. Create alert rules to monitor the health and success of your backup procedures.