19.02.2026

Zero-Downtime Database Migrations

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Database migrations strike fear into the hearts of operations teams. Extended maintenance windows, potential data loss, and angry users are all too common outcomes. But with the right approach, you can migrate even petabyte-scale databases without a single second of downtime.

Why Zero-Downtime Matters

Modern applications demand 24/7 availability. A multi-hour maintenance window for database migration can cost businesses millions in lost revenue and erode user trust. The goal is to make migrations invisible to end users.

The Core Technique: Dual-Write with Replication

The foundation of zero-downtime migrations relies on three principles:

Consistent snapshots: Take a point-in-time copy without locking the database
Change data capture (CDC): Continuously replicate changes from source to target
Transparent cutover: Switch traffic with minimal query buffering

Step-by-Step Migration Process

1. Initial Data Copy

Start with a consistent, non-locking snapshot of your source database. Tools like pg_dump with --no-lock or MySQL's mysqldump with --single-transaction enable this without blocking writes.

2. Set Up Replication

Configure CDC to stream changes from source to target. Popular options include:

# Debezium for Kafka-based CDC
docker run -d debezium/connect:latest

# Or native logical replication in PostgreSQL
CREATE PUBLICATION migration_pub FOR ALL TABLES;

3. Verify Data Integrity

Run checksums or row-count comparisons between source and target. Never skip this step.

4. Traffic Switchover

Route application traffic through a proxy that can buffer queries briefly during cutover. The actual switch typically takes under one second.

5. Reverse Replication

Maintain the ability to cut back to the original system. Keep reverse replication running until you are confident in the new setup.

Tools Worth Knowing

Vitess: Used by YouTube and Slack for MySQL sharding and migrations
gh-ost: GitHub's online schema migration tool
pglogical: Logical replication for PostgreSQL cross-version migrations
AWS DMS: Managed service for heterogeneous database migrations

Operational Tips

Plan migrations during low-traffic periods even with zero-downtime techniques. Monitor replication lag closely and set alerts for any drift. Always have a rollback plan that has been tested in staging.

Conclusion

Zero-downtime database migrations are achievable at any scale with proper planning. The combination of consistent snapshots, CDC replication, and transparent cutover lets SRE teams migrate confidently without impacting users.

Looking to automate your infrastructure operations? Akmatori provides AI-powered agents that help SRE teams manage complex tasks like migrations with confidence. Built on Gcore's global infrastructure, Akmatori brings intelligent automation to your operational workflows.

Akmatori team