Blue-green deployment is a deployment strategy that enables zero downtime online through dual-environment switching. The core is to prepare two sets of the same environment (blue is the old version and green is the new version). After the new version is tested correctly, the traffic will be switched to the new environment through load balancing, thereby achieving seamless updates and rapid rollback. Advantages include: 1. Supports rapid rollback; 2. Suitable for scenarios where large changes or zero downtime are required; 3. Improve system stability. Key implementation points: 1. Ensure environmental consistency; 2. Configure traffic switching mechanisms (such as Nginx, Kubernetes Service); 3. Health check; 4. Handle database compatibility. Operation process: 1. Deploy a green environment; 2. Test and verify; 3. Switch traffic; 4. The original blue environment can be retained or recycled. When using it, you need to pay attention to issues such as DNS cache, log monitoring synchronization, and CDN cache processing.

The new version is launched without any pitfalls, and the blue and green deployment is actually quite practical. Many people think this thing sounds high-end, but in fact, it is not difficult to operate after understanding the principles. The key is to control the pace of traffic switching and ensure that service is not interrupted.

What is blue-green deployment?

Simply put, it is to prepare two sets of the same environment, one is the running "blue" environment, and the other is the new version of the "green" environment. You can cut traffic from the old environment after the new environment is fully ready. The benefits of doing this are obvious: it can quickly roll back when something goes wrong, and it will not affect the user's use.

To give the simplest example: you have an online application running on Server A, and now you want to launch a new feature. You first deploy the new version on server B, and after the test is no problem, then cut the traffic from A to B. If there is any problem with the new version, just switch back immediately.

Why use blue and green deployment?

There are several scenarios that are particularly suitable:

• New version with major changes online
• Need zero downtime service
• Systems with high rollback mechanism requirements

Compared to directly replacing the code or rolling updates, the biggest advantage of blue and green is its strong reversibility to switch . Especially when facing unknown bugs, it can give you a way out and not force yourself to take it online.

Key points for implementing blue and green deployment

To succeed, these places cannot be ignored:

• Environment consistency : The configurations of the two environments must be consistent, including dependencies, permissions, network settings, etc.
• Load balancer/reverse proxy configuration : You need to have a mechanism that can quickly switch traffic, such as Nginx, HAProxy or routing functions provided by cloud service providers.
• Health check mechanism : Confirm whether the new version is operating normally before switching to avoid attracting traffic to bad services.
• Database processing method : If database changes are involved, compatibility must be considered. New and old versions may read and write a table at the same time, and problems may occur if the structure changes.

For example, if you add a field, the old version may not be recognized. At this time, it will either be compatible or you can only switch the database structure at one time.

How to operate blue and green deployment?

The specific operations of different platforms are slightly different, but the general process is similar:

• Prepare the new version of the deployment environment (Green)
• Deploy and test in a new environment
• No problem checking health status
• Cut traffic from Blue to Green
• The original Blue environment can be retained as a backup or recycled resources

Some companies will use Blue and Green alternately, so that they do not need to rebuild the environment every time they go online. If you use Kubernetes, you can use Service and Label to implement similar logic; if it is a cloud platform, AWS has special deployment strategy support.

Tips: Don't be fooled by details

• Don't forget the DNS cache issue. Sometimes the client caches the IP, but after switching, it still connects to the old service.
• Logs and monitoring should be tracked simultaneously in the new environment, otherwise it will be difficult to locate problems.
• If you use CDN, remember to clean the cache or do grayscale refresh.

Basically all that is it. The blue-green deployment is not complicated, but some details are easily overlooked. Plan the environment and switching process in advance, and you will feel much more at ease when you go online.

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