Using blue-green deployment to reduce downtime
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Blue-green deployment is a technique that helps you reduce app downtime and risk by running two identical production environments: “Blue” and “Green.”
At any time, only one of the environments is live, with the live environment serving all production traffic.
For the example discussed here, Blue is live and Green is idle. As you prepare a new version of your software, deployment and the final stage of testing takes place in the environment that is not live: in this example, Green. After deploy and fully tested the software in Green, you switch the router so that all incoming requests now go to Green instead of Blue. Green is now live, and Blue is idle.
This technique can eliminate downtime due to app deployment. In addition, blue-green deployment reduces risk: if something unexpected happens with your new version on Green, you can immediately roll back to the last version by switching back to Blue.
You can adjust the route mapping pattern to display a static maintenance page during a maintenance window for time-consuming tasks such as migrating a database. In this scenario, the router switches all incoming requests from Blue to Maintenance to Green.
Important If your app uses a relational database, blue-green deployment can lead to discrepancies between your green and glue databases during an update. To maximize data integrity, configure a single database for backward and forward compatibility.
For this example, consider a simple app: “demo-time.” This app is a webpage that displays the words “Blue time” and the date/time on the server.
Use the Cloud Foundry Command Line Interface (cf CLI) to push the app. Name the app “Blue” with the subdomain “demo-time.”
$ cf push Blue -n demo-time
As shown in the graphic:
- Blue is now running on Cloud Foundry.
- The Cloud Foundry Router sends all traffic for
demo-time.example.comtraffic to Blue.
Now make a change to the app.
1. Replace the word “Blue” on the webpage with “Green,” then rebuild the source file for the app.
cf push again, but use the name “Green” for the app and provide a different subdomain to create a temporary route:
$ cf push Green -n demo-time-temp
After this push:
- Two instances of the app are now running on Cloud Foundry: the original Blue and the updated Green.
- The Cloud Foundry Router continues sending all traffic for
demo-time.example.comto Blue. The router now also sends any traffic for
Now that both apps are up and running, switch the router so all incoming
requests go to both the Green app and the Blue app.
Use the cf map-route command to map the original URL route (
demo-time.example.com) to the Green app.
$ cf map-route Green example.com -n demo-time Binding demo-time.example.com to Green... OK
cf map-route command :
- The Cloud Foundry Router continues sending traffic for
- Within a few seconds, the Cloud Foundry Router begins load balancing traffic for
demo-time.example.combetween Blue and Green.
After you verify that Green is running as expected, stop routing requests to Blue using the cf unmap-route command:
$ cf unmap-route Blue example.com -n demo-time Unbinding demo-time.example.com from blue... OK
cf unmap-route command:
- The Cloud Foundry Router stops sending traffic to Blue.
Now all traffic for
demo-time.example.com is sent to Green.
You can now use
cf unmap-route to remove the route
demo-time-temp.example.com from Green. You can delete the route using
cf delete-route or reserved it for later use. You can also decommission Blue, or keep it in case you need to roll back your changes.
Cloud Foundry community members have written a plug-in to automate blue-green deployment:
- BlueGreenDeploy: cf-blue-green-deploy is a plug-in, written in Go, for the Cloud Foundry Command Line Interface (cf CLI) that automates a few steps involved in zero-downtime deployments.