How to Enhance Phased Rollouts with Feature Flags

When releasing a new feature, the best practice is to roll it out to segments of your user base at a time, rather than giving everyone access at once—this is called a phased rollout. Feature flags make it easier than ever to conduct phased rollouts, analyse the results, and enable continuous delivery.

What are phased rollouts?

A phased rollout is a deployment strategy where new features or system updates are released incrementally to different user segments, rather than pushed to your entire user base in one go.

Each phase acts as a controlled test, allowing teams to gather valuable feedback, monitor system stability, and make necessary adjustments before full deployment. For many organisations—particularly those in regulated industries or running high-traffic applications—a phased rollout approach is the most reliable path to a successful implementation.

Which rollout strategy should I use?

It's tempting to think of a feature release as simply flipping a switch. In reality, developers choose between several strategies to protect the user experience and minimise risk. There are three key methods worth understanding:

1. Big bang rollouts
2. Parallel rollouts
3. Phased rollouts

Here they are in greater detail.

Big bang rollouts

Big bang rollouts involve releasing a new feature or switching to a new system all at once—updates go live everywhere at a fixed point in time.

The upside is speed: you can start seeing ROI immediately, and the planning process is relatively straightforward.

However, the downside is significant. No matter how thorough your testing, you can't anticipate every potential issue that emerges in production. When something goes wrong with a big bang release, it affects your entire user base simultaneously, making it much harder to respond quickly and contain the damage. A contingency plan isn't optional here—it's essential.

Big bang rollouts work best when exposure is limited, such as an internal tool being adopted by one or two teams. For anything customer-facing or mission-critical, the risk is rarely worth it. The CrowdStrike incident in July 2024—where a single update caused failures across 8.5 million Windows devices and an estimated $3 billion in losses—is a stark reminder of what's at stake.

Parallel rollouts

In the parallel method, the new system and the old system run simultaneously, giving your team the ability to learn the new tool at their own pace without immediately losing access to the processes they already know.

It's slower than a big bang rollout, but the safety net of the legacy system reduces risk. The trade-offs are real, though. Running two systems is expensive, and keeping data consistent across both is operationally demanding.

There's also the adoption problem: when users can still access the old system, it's easy to resist the new one. Parallel rollouts tend to work best for large-scale migrations where user satisfaction and business continuity can't be compromised during transition.

Phased rollouts

Phased rollouts release new features to defined user segments over time, rather than deploying to everyone at once. Only a small percentage of users are exposed during the initial phase, which limits the blast radius if something goes wrong.

The most common phased rollout approach starts with the team that built the feature, then expands to the wider internal team, then a beta group of early adopters, and finally the full user base. At each stage, you gather real-time feedback, monitor performance metrics, and make adjustments before progressing. This feedback loop is what makes phased rollouts so powerful—and so much safer than the alternatives.

What are the benefits of phased rollouts?

Phased rollouts have become a standard part of the development process for good reason. They give developers the control to release on their own schedule, test in production safely, and enable continuous delivery without the anxiety of a big bang release. Even though each rollout takes longer, the benefits significantly outweigh the additional time.

Release at your pace

Some features require additional capacity in hardware, infrastructure, or support. Phased rollouts let you scale in line with what your team can realistically handle, reducing the risk of being caught flat-footed by unexpected demand.

Test in production

Staging environments can only tell you so much. By releasing to a small percentage of real users and monitoring the results, you can validate that a feature behaves as expected under actual conditions—catching edge cases and performance issues that controlled testing environments often miss.

This is the core principle behind canary deployment. Like a canary in a coal mine, a small group of users acts as an early warning system. If an issue surfaces, you can roll back immediately—before most of your user base is even aware the feature existed. Phased rollouts also embed testing into the rollout process itself, so it's never an afterthought.

Understand user behaviour

Phased deployment gives product teams a deeper understanding of how different user segments actually interact with new features. Rather than inferring user behaviour from aggregate data post-launch, you can observe it at each stage and use those insights to shape subsequent phases.

This isn't just useful for the feature in question, it builds a clearer picture of user needs that informs the planning and prioritisation of additional features down the line.

More accurate planning

Rolling out in phases gives you real data on capacity and bandwidth requirements before committing to full deployment. After your initial exposure to a small user group, you'll have a much clearer idea of what infrastructure is needed to support broader rollout—which means fewer surprises and more accurate planning across the board.

Phased rollouts also make support more manageable. Only a subset of users are exposed at any given time, so your team can monitor and respond to support requests without being overwhelmed. This makes it easier to prepare for each subsequent phase with confidence.

Enable continuous delivery

Continuous delivery depends on your ability to ship small, frequent updates with minimal risk. Phased rollouts are a natural fit: they allow teams to keep the deployment process moving while maintaining tight control over what end users actually see.

Rather than batching changes into large, infrequent releases, you can iterate continuously and adjust based on feedback at every stage.

How to plan a phased rollout

A successful rollout doesn't happen by accident, it's the result of careful planning before a single user sees the feature. The planning process should begin well before the implementation phase, with clear objectives defined for each stage and agreed success criteria that tell you when it's safe to move forward.

One of the most common challenges teams face is scope creep: adding extra functionality mid-rollout, which introduces new variables and makes it harder to attribute issues to a specific change.

Keep each phase focused on a limited scope, and resist the temptation to bundle in unrelated updates.

Clear communication across engineering, product, and support teams is equally important—everyone should know what's being released, to whom, and when.

Feature flags are the most practical mechanism for managing this process. With a tool like Flagsmith, you can control exactly which users see a feature at any point, adjust percentages without redeploying, and roll back instantly if something goes wrong.

• Phase 1: Internal team. Release to the developers who built the feature. This is your lowest-risk initial exposure and lets you catch obvious issues before anyone else is affected.
• Phase 2: Wider organisation. Expand to the full internal team. Regular check-ins at this stage can surface usability issues that only emerge with a broader, less technically-minded user group.
• Phase 3: Beta users / early adopters. Open to a defined group of external users who've opted in to early access. It’s at this stage that you gather the most valuable user feedback: constructive, real-world responses from people who actually want to engage with what you've built.
• Phase 4: Percentage-based rollout. Begin expanding to your wider user base, starting at around 1–5% and increasing incrementally. Monitor key performance indicators at each increment before pushing further.
• Phase 5: Full deployment. Once each preceding phase has passed its success criteria, complete the rollout to 100% of users and retire the feature flag.

Before each phase begins, establish which performance metrics you'll track and what thresholds indicate a problem. These should include system stability indicators—error rates, latency, crash reports—alongside user satisfaction signals like engagement, retention, and support ticket volume. Having this data defined in advance makes it far easier to make objective decisions about whether to advance, pause, or roll back.

What are the best practices for phased rollouts?

For many organisations, phased rollouts are the default approach for any significant update. To get the most from them, keep these best practices in mind.

Determine your deployment path

Map out your rollout process before you start. Know which user segments will receive access at each phase, and define the criteria that allow you to move from one phase to the next. 

By taking this step, you remove ambiguity and give both engineering and product teams a shared understanding of what a successful rollout looks like.

Keep your user segments simple

Overly complex segmentation is one of the most common challenges teams run into. Start simple—internal team, beta users, and a percentage of the broader user base—and layer in additional segmentation once you're comfortable with the process. The added benefit is that performance data becomes much easier to interpret.

Make incremental changes

Avoid bundling large application changes into a single feature flag. Smaller, more focused updates are easier to test, easier to roll back, and produce cleaner data. The more isolated a change, the more confidence you can have in attributing results directly to it.

Make sure you have enough traffic

The value of phased rollout data depends on having enough traffic to draw meaningful conclusions.

For A/B testing, you'll need sufficient volume to achieve statistical significance; for API testing, you'll need enough load to validate that the system scales.

If traffic is limited, qualitative methods like user interviews and surveys can supplement the data you're collecting.

Track the right metrics

Define your key performance indicators before the rollout begins. Track both technical metrics—error rate, response time, system stability, request throughput—and user-facing metrics—engagement, task completion, navigability, and satisfaction.

Always capture baseline metrics before launch so you have a meaningful point of comparison.

Consider the impact of divergent experiences

When different user groups are using different versions of your software simultaneously, it can cause confusion—particularly for customer support teams trying to reproduce issues.

Be thoughtful about which features are visible to which segments, and avoid making changes so significant that users notice something is different from what their colleagues or peers are seeing.

Enable phased rollouts with Flagsmith

Flagsmith lets you define your user segments and control feature access against those segments, all from a single dashboard, without any redeployment. Whether you're managing a simple internal rollout or a complex, multi-phase deployment across millions of users, Flagsmith integrates with your existing tech stack and gives you the real-time feedback and control you need to release with confidence.

Get started for free and run your next phased rollout the right way.