Comparing deployment strategies: Canary, blue-green, and rolling
Software deployment has changed a lot over the last few years, and if you’re just peeking in, you might not be familiar with some of the latest vocabulary.
Let’s dive in. In this article, we’ll go over rolling, blue/green, and canary deployment strategies, plus some pros and cons of each.
Blue-Green Deployment Strategy
What is Blue-Green Deployment Strategy?
Blue-green deployment is a release strategy that is useful for updating applications without downtime.
How it works: A team maintains two identical production application instances behind a load balancer or service mesh. One of the production applications hosts the current production, while the other is held in reserve.
When a new application version is deployed to the reserve infrastructure–the “green” environment–it undergoes testing. At the same time, user traffic continues to be routed to the active “blue” environment.
Once testing is completed the new version is considered ready. Traffic switches over to the earlier “green” environment. The previous “blue” environment serves as a backup in case of any issues with the new version.
Blue-Green Deployment Strategy – pros and cons
- Zero downtime: Blue-green deployment switches between two similar sites so that customers can move seamlessly from one to the other without any interruption.
- Easy and quick rollback: If there is an issue with the new release, the old version can easily be switched back with just a load balancer switch.
- Allows testing of old vs. new versions: The strategy will enable developers to test an app or site’s old and new versions, making it perfect for disaster recovery practices.
- Lower downtime costs: Blue-green deployment allows app updates to be deployed without costly company downtime schedules. Thanks to low-traffic windows, developers can deploy updates whenever they’re ready.
- High infrastructure costs: It requires double the resources, which can increase infrastructure costs significantly. It can be a significant barrier for small companies or those with limited budgets.
- Not suitable for minor version changes: Blue-green deployments are designed for significant updates and revisions. If you only need to make a small change to your app, this deployment strategy may be too complex and costly to implement.
- The complexity of replication: Replicating a production environment can be complex, especially when working with microservices. This complexity can lead to errors or inconsistencies that may not be identified until after the deployment.
- Need for testing and monitoring: The green instance must be tested and monitored thoroughly before it can be released to production. It requires additional resources and can add to the overall deployment time.
Why might you choose a blue-green deployment strategy?
Blue-green deployment is ideal when major overhauls come with each new product release.
This also comes with high infrastructure costs, as you’ll effectively maintain two identical hosting environments.
That said, zero downtime, easy rollbacks, and the ability to save the previous version for future developments make blue-green deployments attractive for a lot of organizations. This is especially true for rapidly evolving SaaS applications.
To use a blue-green development strategy effectively, you’ll need to deploy your application twice and run it on systems that are as identical as possible.
When the environment where you’re staging updates is in standby mode, you can temporarily take it offline to deploy an update. This means that the production environment remains active for all visitors while the new environment is updated with the latest content.
Canary Deployment Strategy
What is Canary Deployment Strategy?
Canary deployment is a deployment pattern that allows developers to test new features or changes on a subset of users or servers before releasing them to an entire user base.
How it works: In canary deployments, a team conducts staged releases to solicit instant feedback from users. This way the team gradually implements a new version of the software.
The team starts with a small percentage of users. It then moves on to a larger audience once the development team verifies that the canary instance works correctly.
The intent of a canary deployment is to cut down on software downtime and possible crashes. It also makes it easy to roll back changes that are loaded with bugs.
Canary deployments usually come with a number of critical steps: sharing the current version, splitting users, testing the new version, deciding on the implementation, and sending 100% of user traffic to the new version if it meets the expectations.
We go into depth on canary deployments in our article: How canary deployment is fast, powerful, and good for your users.
Canary Deployment Strategy – pros and cons
- Reduced risk of losing users: Canary deployment minimizes the risk of losing users by allowing you to quickly revert to the previous version if the new changes don’t appeal to them.
- Customer satisfaction: This approach helps you get valuable feedback from real application users, meaning you can better respond to their needs.
- Performance testing: You can test the canary version on a fraction of your users, then easily predict the capacity to scale the system to full size.
- No downtime: As canary deployments only affect a small group of users, you don’t have to worry about software downtime.
- Quick deployment of new changes: With canary deployment, you can start analyzing the results of real users without waiting for your team to run lengthy tests.
- Fast and easy rollback: If the changes contain bugs or don’t appeal to your users, you can quickly restore the previous version.
- Risk of losing some of your users: Canary instance users may encounter bugs or may not like the new version.
- Difficult to deploy on local devices: Canary deployment is challenging to deploy on personal devices.
- Time-consuming process: Creating and analyzing a canary deployment requires time and effort from the software development team.
- Implementation difficulty: Canary deployment requires changing the database schema to support several application instances, which can be a challenge for teams with limited experience.
- Complicated database changes: Reviewing changes in a database can get complex.
When should you consider using a canary deployment strategy?
A canary deployment strategy can be pretty great for companies who provide cloud-based solutions. This is because cloud solutions can be updated remotely and already have active users.
Canary deployment is also great for teams who update software frequently, as well as products with a large user base.
And, let’s be honest: How well a team operates can also be a factor. If each change takes a long time to implement, or if users are unsubscribing due to software bugs, it might be worth looking into canary deployments.
Rolling Deployment Strategy
What is Rolling Deployment Strategy?
A rolling deployment is a way to update a distributed application.
How it works: With rolling deployments, a team limits updates to a subset of application instances at a time, instead of updating all instances simultaneously.
This approach offers flexibility in scaling up a new version before scaling down an old version. It also limits the number of unavailable application instances during a scale-up.
Rolling deployments reduce risks when deploying new features, and can cut down on downtime. Teams using rolling deployments only redirect traffic to a new version when it’s ready.
That said, rollbacks can be slow, and may need to be conducted gradually. New deployments need to be backward compatible so that they can coexist with earlier versions.
Rolling Deployment Strategy – pros and cons
- Minimal downtime: Batch deployments mean less downtime. Traffic is redirected to the new version only when it’s ready.
- Reduced risk: As, again, these are batch deployments, there’s less of a risk of flawed updates affecting a large number of users. This approach also ensures that the new deployments are backward compatible and coexist with old versions.
- Flexibility: Rolling deployment offers flexibility as the team can stagger change releases and monitor new environments while the old ones are still updating. This approach also allows for easy rollback to a previous version during deployment.
- Scalability: Rolling deployment may not be ideal for applications that require a high level of scalability. Since this approach requires upgrading nodes in batches, it may not be able to handle surges in traffic that can occur when multiple nodes are offline.
- Backward Compatibility: Sometimes backwards compatibility can mean complex code maintenance. Developers have to make sure new and old versions of the application work together, which can be challenging if the update involves significant changes.
- Complexity: Managing a rolling deployment can be complex, especially if the application has many nodes. Monitoring the deployment and coordinating the different stages can require high attention and effort, increasing the likelihood of human error.
- Slow Deployment: Rolling deployments can take a longer time to deploy since they’re, again, done in batches. The incremental approach can slow down the overall deployment process, which may not be ideal for applications that require a fast rollout.
When should you consider using a rolling deployment strategy?
Rolling deployments might be a great fit if your company has a hosting infrastructure with enough capacity to take some servers out of service without any decrease in performance.
They’re also good for companies that can handle some being offline if something goes wrong during the update. If you anticipate updating an app with small changes, often, rolling deployments might make a lot of sense.
Blue-green, Canary and Rolling: Which deployment strategy is worth choosing?
Like most tech, there isn’t really a one-size fits all approach to software development. Often it comes down to your team, its needs, and its budget.
If you’re in the mood for experimenting with feature releases, check out Unleash feature management.
It’s free to try, and it’s a great way quickly release new features to a small subset of users or servers and monitor their performance.