Blue-Green Deployment for Software Applications: Pros and Cons
What Is Blue-Green Deployment?
A blue-green deployment is a software release model that transfers traffic from a current version to a new version. It involves using two almost identical production environments, called blue and green. Only one environment remains live and handles all production traffic.
Organizations use progressive delivery strategies like blue-green deployment to avoid downtime and minimize risks during updates. Modern development methodologies prioritize speed, quality, security, and reliability. To meet these standards, organizations utilize continuous integration and continuous deployment (CI/CD) pipelines that enable a highly automated and efficient process.
CI/CD pipelines help meet software testing and stability standards while frequently releasing software updates to ensure a positive customer experience. A blue-green deployment helps organizations to continuously improve their products without compromising the user experience.
How Does Blue-Green Deployment Work?
Automating a deployment requires transferring software from the testing environment to production, ideally with minimal downtown. Blue-green deployments have two almost identical environments, allowing an easier transition between the testing and the live environment.
Testing occurs in the “green” environment, while the “blue” environment hosts the live application. Once you’ve finished testing, you redirect traffic to the test environment, which now becomes the production environment, while the blue environment becomes the new test environment. Traffic can be routed between the environments using a traditional load balancer or a more advanced technology such as a service mesh.
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This approach enables quick rollbacks, allowing you to keep the blue environment as a backup when you switch to the green (new) one. For example, you might run your app in read-only mode during testing and switch to read-write mode when live. The two environments should be as similar as possible to ensure a seamless transition. They can share an IP address.
When the environment is stable, you can start testing. This stage involves deploying the green environment as the staging environment. You deploy the next release in the green environment, with the blue becoming a backup. This approach lets you continuously test the disaster recovery system.
Blue-Green Deployment Benefits
Here are the main advantages of a blue-green deployment approach.
Having a Backup System
Blue-green deployments provide a reliable backup system with one server constantly on standby to take over if the live system fails. This powerful risk management strategy is why organizations choose a blue-green deployment. Issues unrelated to new software updates can occur when one server is live—these might indicate the presence of malware or an attacker targeting the host server.
Blue-green deployments require replicating all application infrastructure, allowing back-end developers to redirect traffic to the standby version quickly. Your organization can remain functional and provide services while you fix the issues on the other server. This backup system gives you an extra level of confidence.
Blue-green deployments are a great way for a product owner to release software to production using a CI/CD framework. DevOps teams can release updates anytime with minimal disruption—implementing the release is usually as simple as changing the routing. No downtime is involved, so your deployments won’t negatively impact your users.
Teams can push releases without scheduling extra hours or accounting for lost revenue due to downtime. They can implement updates properly without rushing, minimizing stress and error.
Like releases, reversing or rolling back an update is simple and fast. Blue-green deployments have two production-ready environments, allowing you to quickly switch to the more stable backup environment if issues arise in the live environment. A common way to identify issues in production is Kubernetes health checks.
Fast rollbacks reduce the risk associated with experimenting in your production environment. Teams can quickly remove issues by routing traffic back to the standby environment. The main risk here is the loss of user transactions, but it is possible to manage this risk.
You could temporarily set the application to read-only during the cutover. Alternatively, you might implement rolling cutovers using a load balancer while waiting for the transactions to complete in your live environment.
Downtime can result in lost business productivity and negatively impact the end user’s experience because the application becomes unavailable. For critical services, the cost of downtime can be prohibitive, especially when it affects a large platform online with many transactions.
Blue-green deployments allow your organization to avoid downtime typically associated with fixing a problem. You can switch users to the backup environment without them noticing while fixing recurring issues or carrying out maintenance checks. Other deployment models often require fixes and upgrades during off-peak hours when traffic is low. Even with lower demand, downtime can be inconvenient for customers.
Testing in a Realistic Environment
Testing in production allows you to check your product’s functionality while it is live on the server. It allows you to see how the software functions from the UI. However, it is often difficult and can impact user experience when you find bugs before you can fix them. A blue-green deployment lets you test the product on an inactive server while users can continue accessing the application on the live server.
This approach minimizes the risk of unexpected issues during production because you can test and eliminate them in a near-identical environment without the user’s knowledge. Testing in production allows your organization to preserve its professionalism and public reputation.
What Are the Drawbacks of Blue-Green Deployments?
Despite the various benefits of blue-green deployments, they may also have some additional challenges and costs involved.
Complexity of Infrastructure
Deciding on a blue-green deployment process requires making trade-offs. Although you eliminate downtime, these deployments can be complex to manage because they require a continuous integration server and constant rerouting of network traffic.
For example, when you serve a “blue” instance, the continuous delivery pipeline must push traffic to the green environment (or vice versa if you’ve switched). Some deployment platforms offer solutions, but this is an important challenge to consider.
Complexity of Deployments
A blue-green deployment ideally allows you to safely and easily roll back changes if there are issues with a release. In reality, it isn’t always possible to implement a simple rollback. For instance, if several applications share a database and the release has a schema dependency, you might not be able to roll it back without migrating the schema.
While you can usually deal with these issues, they add more complexity than a standard deployment with downtime. Blue-green deployments have more moving parts and more things to automate, providing more opportunities for error. You must invest in CI/CD skills and tools to help manage this complexity.
Scaling and Cost Considerations
When you maintain more than one instance of an application, it is important to consider the extra costs associated with hosting a second production environment. The cost might outweigh the benefits for some use cases.
For example, the costs might sharply increase if you use a microservices architecture or host several applications. In such cases, you might prefer a modified form of blue-green deployment that eliminates downtime without paying for the full costs of hosting two environments (i.e., removing the old version after you evaluate the deployment).
In this article, I covered some key pros and cons of blue-green deployments:
- Having a Backup System
- Rapid Releases
- Easy Rollbacks
- Zero Downtime
- Testing in a Realistic Environment
- Complexity of Infrastructure
- Complexity of Deployments
- Scaling and Cost Considerations
I hope this will be useful as you adopt more sophisticated, progressive delivery strategies for your software projects.
Disclaimer: The author is completely responsible for the content of this article. The opinions expressed are their own and do not represent IEEE’s position nor that of the Computer Society nor its Leadership.