The Art of Always-On: How We Maintain Millions of Users While Updating Software and Infrastructure (Part 1 of the Series)

In today’s connected world, users expect instant access, seamless updates, and zero downtime. For software platforms serving millions globally, staying online 24/7 while rolling out new features, database changes, and infrastructure upgrades is akin to walking a tightrope as an engineer.

This blog series examines how large-scale online systems are maintained without interruption. In Part 1, we break down the foundational principles and strategies that keep everything running smoothly, even as things constantly change behind the scenes.

Why Always-On Systems Are Non-Negotiable

Downtime equals loss of users, revenue, and reputation. Especially in sectors like finance, gaming, SaaS, and e-commerce, even a minute of downtime can lead to cascading issues. This forces teams to architect systems that can evolve while they are in use.

The Core Challenge: Change Without Disruption

Imagine changing the wheels of a car while it’s speeding down the highway. That’s essentially what happens during live database schema migrations, feature rollouts, or server upgrades. Here’s how we make it possible.

1. Decoupled Architecture

Modern platforms are increasingly microservice-based. Instead of a single monolithic block, services are divided into self-contained units that can be deployed, monitored, and scaled independently. This decoupling means changes in one part don’t bring down the whole.

Example: Want to update the login logic? If authentication is its service, you can test and roll out changes without affecting game sessions, transaction handlers, or analytics pipelines.

2. Blue-Green & Canary Deployments

We never deploy blindly. Blue-green deployment lets us shift live traffic between two nearly identical environments (blue and green). One gets updated, and then traffic is gradually or instantly routed to it based on risk tolerance.

Canary deployments go further by releasing updates to a small percentage of users first. If performance drops or errors rise, we roll back before mass impact.

3. Database Change Management

Databases don’t take kindly to abrupt changes. We follow these key rules:

• Backward-compatible migrations: Deploy schema changes that work with both old and new application code.

• Versioned scripts: Every DB change is tracked with version control, and rollback scripts are included.

• Shadow tables: For major shifts, we write data to both the old and new formats temporarily and switch only when the new path is verified.

4. Feature Flags Everywhere

Feature flags enable us to toggle functionality on or off without requiring a code redeployment. We can help a new interface for internal staff first, then 5% of users, then everyone. This ensures stability while testing in production.

5. Observability: Metrics, Logs, Traces

You can’t fix what you can’t see. We rely on:

• Metrics to track user experience (latency, errors, conversions)

• Structured logs for debugging across services

• Distributed tracing to see precisely where a request breaks

If something goes wrong, alerts are triggered immediately via Slack, SMS, or incident dashboards.

6. Resilience Engineering

Even the best updates can fail. That’s why we:

• Build retries and circuit breakers into every API call

• Auto-scale services during traffic spikes

• Use queues to buffer the load

• Plan for rollback and failover in every change plan

7. Communication and Change Windows

Product managers, devs, SREs, and QA work from the same release calendar. High-risk changes occur within agreed-upon windows, typically during low-traffic hours. And if it's truly 24/7 global traffic? We still have time to minimize the impact regionally.

Coming Up Next

In Part 2 of this series, we’ll dive deeper into live database migrations: how to update live data structures with zero downtime, and the secret sauce to avoiding corrupted data and user frustration.

Maintaining millions of users while updating live systems is both an art and a science. With the exemplary architecture, discipline, and culture, it becomes not only possible but predictable.

Stay tuned.