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title: Using Blue-Green Deployment to Reduce Downtime and Risk
owner: Routing
<strong><%= modified_date %></strong>
Blue-green deployment is a technique that reduces downtime and risk by running
two identical production environments called Blue and Green.
At any time, only one of the environments is live, with the live environment
serving all production traffic.
For this example, Blue is currently 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,
Once you have deployed and fully tested the software in Green, you switch the
router so 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 application 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.
<p class="note"><strong>Note</strong>: If your app uses a relational database, blue-green deployment can lead to discrepancies between your Green and Blue databases during an update. To maximize data integrity, configure a single database for backward and forward compatibility.</p>
<p class="note"><strong>Note</strong>: 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.
## <a id='blue-green-deployment'></a>Blue-Green Deployment with Cloud Foundry Example ##
For this example, we’ll start with a simple application: "demo-time."
This app is a web page that displays the words "Blue time" and the date/time on
the server.
### <a id='push-an-app'></a>Step 1: Push an App ###
Use the Cloud Foundry Command Line Interface (cf CLI) to push the application.
Name the application "Blue" with the subdomain "demo-time."
<pre class="terminal">
$ cf push Blue -n demo-time
As shown in the graphic below:
* Blue is now running on Cloud Foundry.
* The CF Router sends all traffic for `` traffic to Blue.
<%= image_tag("../images/blue-green/blue.png") %>
### <a id='update-and-push'></a>Step 2: Update App and Push ###
Now make a change to the application.
First, replace the word "Blue" on the web page with "Green," then rebuild the source file for the application.
Run `cf push` again, but use the name "Green" for the application and provide a
different subdomain to create a temporary route:
<pre class="terminal">
$ cf push Green -n demo-time-temp
After this push:
* Two instances of our application are now running on Cloud Foundry: the
original Blue and the updated Green.
* The CF Router continues sending all traffic for `` to
The router now also sends any traffic for `` to Green.
<%= image_tag("../images/blue-green/blue-green.png") %>
### <a id='map-green'></a>Step 3: Map Original Route to Green ###
Now that both apps are up and running, switch the router so all incoming
requests go to the Green app *and* the Blue app.
Do this by mapping the original URL route (``) to the Green
application using the [cf map-route]( command.
<pre class="terminal">
$ cf map-route Green -n demo-time
Binding to Green... OK
After the `cf map-route` command :
* The CF Router continues sending traffic for `` to Green.
* Within a few seconds, the CF Router begins load balancing traffic for
`` between Blue and Green.
<%= image_tag("../images/blue-green/map.png") %>
### <a id='unmap-blue'></a>Step 4: Unmap Route to Blue ###
Once you verify Green is running as expected, stop routing requests to Blue
using the [cf unmap-route]( command:
<pre class="terminal">
$ cf unmap-route Blue -n demo-time
Unbinding from blue... OK
After `cf unmap-route` command:
* The CF Router stops sending traffic to Blue.
Now all traffic for `` is sent to Green:
<%= image_tag("../images/blue-green/unmap.png") %>
### <a id='remove-temp-route'></a>Step 5: Remove Temporary Route to Green ###
You can now use `cf unmap-route` to remove the route `` from Green. The route can be deleted using `cf delete-route` or reserved for later use. You can also decommission Blue, or keep it in case you need to roll back your changes.
<%= image_tag("../images/blue-green/green.png") %>
## <a id='implementations'></a>Implementations
Cloud Foundry community members have written plugins to automate the blue-green
deployment process. These include:
* [Autopilot]( Autopilot is a Cloud Foundry Go plugin that provides a subcommand, `zero-downtime-push`, for hands-off, zero-downtime application deploys.
* [BlueGreenDeploy]( cf-blue-green-deploy is a plugin, written in Go, for the Cloud Foundry Command Line Interface (cf CLI) that automates a few steps involved in zero-downtime deploys.