Architecture
The Operator
An Operator is a method of packaging, deploying and managing a Kubernetes application. Some applications, such as databases, required more hand-holding, and a cloud-native Postgres requires an operator to provide additional knowledge of how to maintain state and integrate all the components. The StackGres operator allow to deploy a StackGres cluster using a few custom resources created by the user.
Operator availability concerns
Operator availability only affect operational plane, data plane is not affected at all since the database will work as expected when the operator is offline. There is a best effort in maintaining the operator available. It is expected that if at some point the operator is unavailable and this could lead to unavailability of following operational aspects:
- Cluster creation / update
- Cluster configuration creation / update / deletion
- Backups generation
- Reconciliation of modified resources controlled by the operator (when modified by the user or some other means)
Operator unavailability does not affect following functional aspects:
- Database high availability
- Connection pooling
- Incremental backups
- Stats collection
The Cluster
A StackGres cluster is basically a StatefulSet where each pod is a database instance. The StatefulSet guarantees that each pod is always bind to its own persistent volume therefore the database instance data will be mapped to the state of a patroni instance inside kubernetes.
StackGres Cluster Architecture diagram
StackGres Pod Architecture diagram
We use a pattern called sidecar where a main application run in a container and other container are providing a side functionality like connection pooling, export of stats, edge proxying, logging dispatcher or database utilities.
UDS: Unix Domain Socket