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High-availability, Scaling, and Robustness
High availability
The Kong Ingress Controller is designed to be reasonably easy to operate and be highly available, meaning, when some expected failures do occur, the Controller should be able to continue to function with minimum possible service disruption.
The Kong Ingress Controller is composed of two parts: 1. Kong, which handles the requests, 2. Controller, which configures Kong dynamically.
Kong itself can be deployed in a highly-available manner by deploying multiple instances (or pods). Kong nodes are state-less, meaning a Kong pod can be terminated and restarted at any point of time.
The controller itself can be stateful or stateless, depending on if a database is being used or not.
If a database is not used, then the Controller and Kong can be deployed:
- as co-located containers in the same pod and each controller configures the Kong container that it is running with.
- in separate deployments where each can be scaled independently. To learn more about this approach please see the Gateway Discovery section on Deployments page.
For cases when a database is necessary, the Controllers can be deployed on multiple zones to provide redundancy. In such a case, a leader election process will elect one instance as a leader, which will manipulate Kong’s configuration.
Leader election
Multiple Kong Ingress Controller instances elect a leader when connected to a database-backed cluster or when Gateway Discovery is configured. This ensures that only a single controller pushes configuration to Kong’s database or to Kong’s Admin API to avoid potential conflicts and race conditions.
When a leader controller shuts down, other instances will detect that there is no longer a leader, and one will promote itself to the leader.
For this reason, the controller needs permission to create a Lease resource.
By default, the permission is given at Namespace level.
It also needs permission to read and update this Lease.
This permission can be specific to the Lease that is being used
for leader-election purposes.
The name of the Lease is derived from the value of election-id CLI flag
(default: 5b374a9e.konghq.com) and
election-namespace (default: "") as: “
Scaling
Kong is designed to be horizontally scalable, meaning as traffic increases, multiple instances of Kong can be deployed to handle the increase in load.
The configuration is either pumped into Kong directly via the Ingress Controller or loaded via the database. Kong containers can be considered stateless as the configuration is either loaded from the database (and cached heavily in-memory) or loaded in-memory directly via a config file.
One can use a HorizontalPodAutoscaler (HPA) based on metrics
like CPU utilization, bandwidth being used, total request count per second
to dynamically scale Kong Ingress Controller as the traffic profile changes.
Last Known Good Configuration
Prior to Kong Ingress Controller 2.11, new pods will not receive a valid configuration and will be unable to proxy traffic if your Kubernetes API server contains an invalid Kong configuration.
Kong Ingress Controller 2.11 stores the last valid configuration in memory and uses it to configure new pods. Any pods created due to scale out events or pod restarts will receive the latest configuration that was accepted by any Kong pod.
Note: Any changes you make with
kubectlwill not be reflected until the Kubernetes API server state is fixed. This feature is designed to keep your deployment online until an operator can fix the k8s server state.
If the Kong Ingress Controller pod is restarted with a broken configuration on the Kubernetes API server, it will fetch the last valid configuration from an existing Kong instance and store it in memory.
If there are no running proxy pods when the controller is restarted the last known good configuration will be lost. In this event, please fix the configuration on your Kubernetes API server.
