A blue/green deployment strategy provides a method for achieving zero-downtime when you need to run two versions of the same service - a “blue” version and a “green” version - simultaneously. With a blue/green deployment, you can have two, fully-scaled versions of the same service running at the same time on the same cluster. You can then use the load balancer to switch between the two versions as needed.

This type of deployment supports rolling updates where one version of a service can be taken down and upgraded, or rolled back, without disrupting access to the other version of the same service. Similarly, if something goes wrong with one version of a service, you can quickly switch to routing requests to the other version of the service by adjusting the load balancer settings.

Before you begin

Before you create Edge-LB pools and pool configuration files, you should have DC/OS™ Enterprise cluster nodes installed and ready to use, and have previously downloaded and installed the latest Edge-LB packages.

You must have:

Edge-LB installed as described in the Edge-LB installation instructions.
The core DC/OS command-line interface (CLI) installed and configured to communicate with the DC/OS cluster.
The edgelb command-line interface (CLI) installed.
An active and properly-configured DC/OS Enterprise cluster, with at least one DC/OS private agent node to run the load-balanced service and at least one DC/OS public agent node for exposing the load-balanced service.
Enough capacity on the DC/OS Enterprise cluster for two fully-deployed services.

For information about installing Edge-LB packages, see the installation instructions.

Preview of what you’ll do

This tutorial shows how to configure services and load balancing to support a blue/green deployment scenario. In this tutorial, you will:

Create and deploy a load balancing configuration file for a sample web-server application identified as the “blue” version of the service.
Create and deploy a load balancing configuration file for a second, “green” version of the web-server application.
Verify the load balancer is routing traffic successfully to the “blue” version of the service.
Update the Edge-LB configuration to route traffic to the “green” version of the service.
Verify the load balancer routes traffic to the “green” version of the service.
Access the sample application through the public agent IP address and frontend port.

By completing the steps in this tutorial, you can see how to switch to a newer or different version of the same service with zero-downtime, and have the Edge-LB load balancer automatically adjust the traffic routed between the blue and green versions of the service.

Create and deploy the “blue” sample app definition

Copy and paste the following JSON settings to create the sample app definition for the svc-blue service in, and save, the svc-blue.json file:

{
    "id": "/svc-blue",
    "cmd": "/start $PORT0",
    "instances": 1,
    "cpus": 0.1,
    "mem": 32,
    "container": {
        "type": "DOCKER",
        "docker": {
            "image": "mesosphere/httpd"
        }
    },
    "portDefinitions": [
        {
            "name": "web",
            "protocol": "tcp",
            "port": 0
        }
    ],
    "healthChecks": [
        {
            "portIndex": 0,
            "path": "/",
            "protocol": "HTTP"
        }
    ]
}

Create and deploy the “green” sample app definition

Copy and paste the following JSON settings to create the sample app definition for the svc-green service in, and save, the svc-green.json file:

{
    "id": "/svc-green",
    "cmd": "/start $PORT0",
    "instances": 1,
    "cpus": 0.1,
    "mem": 32,
    "container": {
        "type": "DOCKER",
        "docker": {
            "image": "mesosphere/httpd"
        }
    },
    "portDefinitions": [
        {
            "name": "web",
            "protocol": "tcp",
            "port": 0
        }
    ],
    "healthChecks": [
        {
            "portIndex": 0,
            "path": "/",
            "protocol": "HTTP"
        }
    ]
}

Configure load balancing for the “blue” service

Copy and paste the following JSON settings to create the pool configuration file for the sample service in, and save, the sample-deployment-config.json file:

{
  "apiVersion": "V2",
  "name": "sample-deployment-config",
  "count": 1,
  "haproxy": {
    "frontends": [{
      "bindPort": 80,
      "protocol": "HTTP",
      "linkBackend": {
        "defaultBackend": "svc"
      }
    }],
    "backends": [{
      "name": "svc",
      "protocol": "HTTP",
      "services": [{
        "marathon": {
          "serviceID": "/svc-blue"
          },
          "endpoint": {
            "portName": "web"
          }
      }]
    }]
  }
}

Deploy the Edge-LB pool configuration file for the sample service:
```
dcos edgelb create sample-deployment-config
```
Verify deployment of the sample service and obtain the external IP addresses:
```
dcos edgelb endpoints sample-deployment-config
```
The output will resemble this:
```
NAME                   PORT   INTERNAL IPS   EXTERNAL IPS
frontend_0.0.0.0_80    80     172.12.0.189   54.158.195.24
stats                  9090   172.12.0.189   54.158.195.24
```
You can use this output later to verify that the “svc-blue” app is exposed, and to navigate to the public-facing IP address for the public agent node, if your running cluster has more than one public agent node.
Start deployment for the svc-blue.json app definition:
```
dcos marathon app add svc-blue.json
```

Verify deployment status for the “blue” service

Verify the sample-deployment-config.json Edge-LB pool configuration file is configured and deployed correctly:
```
dcos edgelb show sample-deployment-config.json
```
Verify the “svc-blue” app is exposed by navigating to the public-facing IP address for the public agent node:
```
http://<public_agent_public_IP>
```
You don’t need to specify the port in this example because the access to the service is routed through the default port 80 for HTTP traffic. If your DC/OS Enterprise cluster is 1.13, or newer, you can view the public-facing IP address by clicking Nodes in the DC/OS web-based console or by running the following command:
```
dcos node list
```
For more information about how to find the IP address for a public agent, see Finding a public agent IP.

Deploy the “green” version of the sample service

Start deployment for the svc-green.json app definition:
```
dcos marathon app add svc-green.json
```
Verify the blue and green versions of the sample service and the Edge-LB pool instance have been deployed successfully:
```
dcos marathon app list
```

Modify the Edge-LB pool configuration file to point to svc-green by changing the serviceID setting.

    {
      "apiVersion": "V2",
      "name": "sample-deployment-config",
      "count": 1,
      "haproxy": {
        "frontends": [{
          "bindPort": 80,
          "protocol": "HTTP",
          "linkBackend": {
            "defaultBackend": "svc"
          }
        }],
        "backends": [{
          "name": "svc",
          "protocol": "HTTP",
          "services": [{
            "marathon": {
              "serviceID": "/svc-green"
              },
              "endpoint": {
              "portName": "web"
              }
          }]
        }]
      }
    }

Deploy the modified pool configuration file to Edge-LB:
```
dcos edgelb update sample-deployment-config.json
```
Verify the “svc-green” app is exposed by navigating to the public-facing IP address for the public agent node:
```
http://<public_agent_public_IP>
```
If your DC/OS Enterprise cluster is version 1.13, or newer, you can view the public-facing IP address by clicking Nodes in the DC/OS web-based console or by running the dcos node list command.

NOTE: In most cases, the `dcos node list` command returns information that includes both the private and public IP addresses for each node. However, if the Edge-LB pool uses virtual networks, the public and private IP addresses returned might not be accurate.

Phased "Blue/Green" service deployment