Blue-green deployments

Blue-green deployments work by having two identical environments, allowing you to completely switch from one environment to another. Kong Gateway makes this simple by letting you point a Gateway Service at any Upstream entity as a host, where the Upstream entity can have any number of Targets that it can load-balance requests over.

Most commonly, this method is used for running environments in staging and production. When a release is ready in staging, the roles of the two environments switch. The staging environment becomes production, and the production environment becomes staging.

In Kong Gateway terms, for a blue-green deployment you need the following:

• A Gateway Service and a Route
• A blue Upstream and a green Upstream
• Targets configured for each Upstream

You can then toggle the host parameter in the Gateway Service to either Upstream as needed, effectively switching from blue to green and back with one command.

For example, given the following basic Gateway Service, Route, and blue and green Upstreams:

services:
  - name: example-service
    host: blue
    path: "/anything"
    routes:
      - name: example-route
        hosts:
          - "example.domain.com"
upstreams:
  - name: blue
    targets:
    - target: 192.168.34.15:80
      weight: 100
    - target: 192.168.34.16:80
      weight: 50
  - name: green
    targets:
    - target: 192.168.34.17:80
      weight: 100
    - target: 192.168.34.18:80
      weight: 100

This example starts with the Gateway Service pointing to the blue Upstream.

To activate the blue-green switch, you just need to update the host property of the existing Gateway Service. For example, switch the Service host parameter to green:

services:
  - name: example-service
    host: green

In this case, the example uses the default round-robin load balancing, so the green Targets will be queued up in the order they were originally accessed, with weighting applied.

You can switch back and forth between the blue and the green Upstreams at any time, and the switch will be immediate.