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Blue-green upgrade

The blue-green upgrade strategy is a Kong Gateway upgrade option used primarily for traditional mode deployments and for control planes in hybrid mode.

This guide refers to the old version as cluster X and the new version as cluster Y.

Blue-green upgrades are derived from the in-place upgrade strategy. This upgrade strategy benefits from the fact that kong migrations up leaves the database in a state where it can serve requests by either current cluster X or the new cluster Y. The compatibility of the database with cluster X is only lost when kong migrations finish is executed.

This is a more advanced strategy than the dual-cluster upgrade in that there is no need to deploy a new database. It still supports gradually diverting traffic from the current cluster X to the new cluster Y, shown in the following diagram. Furthermore, runtime metrics (for example, Rate Limiting Advanced plugin counters) are sent to the same database. Metrics are continuously collected from both clusters during the upgrade process.

 
flowchart TD
    DB[(Database)]
    CPX(Current 
    Kong Gateway X)
    Admin(No admin 
    write operations)
    Admin2(No admin 
    write operations)
    CPY(New 
    Kong Gateway Y)
    LB(Load balancer)
    API(API requests)

    API --> LB & LB & LB & LB
    Admin2 -."X".- CPX
    LB -.90%.-> CPX
    LB --10%--> CPY
    Admin -."X".- CPY
    CPX -.-> DB
    CPY --"kong migrations up \n (NO kong migrations finish)"--> DB

    style API stroke:none
    style CPX stroke-dasharray:3
    style Admin fill:none,stroke:none,color:#d44324
    style Admin2 fill:none,stroke:none,color:#d44324
    linkStyle 4,7 stroke:#d44324,color:#d44324
    linkStyle 3,6,9 stroke:#b6d7a8

Figure 1: The diagram shows a Kong Gateway upgrade using the blue-green strategy. The new Kong Gateway cluster Y is deployed alongside the current Kong Gateway cluster X. Both clusters use the same database. Traffic is gradually switched over to the new deployment, until all API traffic is migrated.

Compared to dual-cluster and in-place upgrades, blue-green upgrades consume less resources since there is no extra database required, and still allow for no business downtime.

Important: Support from Kong for upgrades using this strategy is limited. Though blue-green upgrades are supported, it is nearly impossible to fully cover all migration tests, because we have to cover all combinations, given the number of Kong Gateway versions, upgrade strategies, features adopted, and deployment modes. If you must use this strategy, only use it to upgrade between patch versions.

In traditional mode, blue-green upgrades are available starting in 2.8.2.x. If you have a Kong Gateway 2.8.x version earlier than 2.8.2.x, upgrade to at least 2.8.2.0 before starting any upgrades to the 3.x series.

Prerequisites

Review the general upgrade guide to prepare for the upgrade and review your options.
You have a traditional deployment or you need to upgrade the control planes (CPs) in a hybrid mode deployment.
You have Kong Gateway 2.8.2.x or later.
You can’t perform dual-cluster upgrades due to resource limitations.

Upgrade using the blue-green method

In the following procedure, kong migrations finish is only executed at the end of the upgrade, after you have verified that the new cluster Y is operating as expected.

The following steps are intended as a guideline. The exact execution of these steps will vary depending on your environment.

Stop any Kong Gateway configuration updates (e.g. Admin API calls). This is critical to guarantee data consistency between cluster X and cluster Y.
Back up data from the current cluster X by following the Backup guide.
Evaluate factors that may impact the upgrade, as described in Upgrade considerations. You may have to consider customization of both kong.conf and Kong Gateway configuration data.
Evaluate any changes that have happened between releases:
- Breaking changes
- Full changelog
Deploy a new Kong Gateway cluster of version Y:
1. Install a new Kong Gateway cluster running version Y as instructed in the Kong Gateway Installation Options and point it at the existing database for cluster X.
  
  Provision the new cluster Y with the same-sized resource capacity as that of the current cluster X.
2. Migrate the database to the new version by running kong migrations up.
  
  Kong Gateway will print a warning log entry that pending migrations exist. This is expected.
3. Start the new cluster Y.
4. Perform staging tests against version Y to make sure it works for all use cases.
  
  For example, does the Key Authentication plugin authenticate requests properly?
  
  If the outcome is not as expected, look over the upgrade considerations and the breaking changes again to see if you missed anything.
Divert traffic from old cluster X to new cluster Y.

This is usually done gradually and incrementally, depending on the risk profile of the deployment. Any load balancers that support traffic splitting will work here, such as DNS, Nginx, Kubernetes rollout mechanisms, and so on.
Actively monitor all proxy metrics.
If any issues arise, roll back by setting all traffic to cluster X, investigate the issues, and repeat the steps above.
Finalize the database migrations with kong migrations finish.
When there are no more issues, decommission the old cluster X to complete the upgrade.

Write updates to Kong Gateway can now be performed, though we suggest you keep monitoring metrics for a while.

Note: This upgrade strategy is not the same thing as the Blue-green (Canary) Deployment. That process is meant for upgrading your upstream services and is not related to Kong Gateway upgrades.

Caution: When adding new plugins to the existing installation (either manually or via the extension of bundled plugins), the kong migrations finish or kong migrations up must be run with the -f flag to forcefully upgrade the plugin schemas.