Managing PostgreSQL High Availability with 'stolonctl' (with examples)

Stolon is an elegant solution for managing high availability of PostgreSQL clusters in cloud-native environments. The stolonctl command-line interface provides a straightforward way to explore and manage a Stolon-managed PostgreSQL setup by interacting with various cluster components. This tool is designed to interact with Stolon clusters, helping administrators to seamlessly check statuses, retrieve data, and update configurations, ensuring the PostgreSQL services remain highly available and resilient.

Use Case 1: Get Cluster Status

Code:

stolonctl --cluster-name cluster_name --store-backend store_backend --store-endpoints store_endpoints status

Motivation:

Knowing the current status of your PostgreSQL cluster is essential to ensure its correct functionality and performance. This command provides insights into whether your servers are up, the replication status, and whether any components need attention. Regular status checks can be integral to maintaining high availability and preemptively addressing any issues.

Explanation:

• --cluster-name cluster_name: Specifies the name of the Stolon cluster you want to query. Identifying the correct cluster is critical, especially in environments managing multiple clusters.
• --store-backend store_backend: Indicates the storage backend used by Stolon, such as etcd or consul, crucial for connecting to the right cluster configuration store.
• --store-endpoints store_endpoints: Provides the endpoints for accessing the store backend, ensuring that stolonctl knows where to fetch the cluster information from.

Example Output:

Cluster View:
Healthy: true 
Master: db1
Standbys: db2

Use Case 2: Get Cluster Data

Code:

stolonctl --cluster-name cluster_name --store-backend store_backend --store-endpoints store_endpoints clusterdata

Motivation:

Retrieving detailed cluster data is necessary for diagnostics and audits. This command reveals different configurations, states, and roles, helping in making informed decisions or troubleshooting any ongoing issues within the cluster.

Explanation:

• --cluster-name cluster_name: Denotes the cluster you’re targeting for data retrieval, allowing you to segregate data from multiple Stolon clusters.
• --store-backend store_backend: Points out the type of storage backend (etcd, consul) being used, ensuring correct cluster communication.
• --store-endpoints store_endpoints: Lists the necessary endpoint addresses to connect to the store backend, directing stolonctl to the appropriate resource locations.

Example Output:

ClusterData:
UID: 1234
Generation: 5
DBs:
DB1, Role: master
DB2, Role: standby

Use Case 3: Get Cluster Specification

Code:

stolonctl --cluster-name cluster_name --store-backend store_backend --store-endpoints store_endpoints spec

Motivation:

Accessing the specification of a Stolon cluster is crucial for understanding its current configurations like database roles, replication factors, and other operational details. This knowledge helps in planning expansions, conducting audits, or managing updates in cluster requirements.

Explanation:

• --cluster-name cluster_name: Identifies the particular Stolon cluster whose specification needs to be extracted, key when dealing with multiple clusters.
• --store-backend store_backend: Defines the storage type of the cluster configuration, ensuring that the system queries the correct source.
• --store-endpoints store_endpoints: Specifies endpoint details for connecting to the necessary backend, necessary for direct access to configuration data.

Example Output:

Specification:
KubeClusterName: postgresql-cluster
Replicas: 1

Use Case 4: Update Cluster Specification with a Patch in JSON format

Code:

stolonctl --cluster-name cluster_name --store-backend store_backend --store-endpoints store_endpoints update --patch 'cluster_spec'

Motivation:

Over time, it might be necessary to adjust the configuration of a Stolon cluster to accommodate changes in workload, optimize performance, or adjust to infrastructure changes. This command allows for dynamic specification updates through a JSON patch, enabling fine-grained control over cluster behavior post-deployment without service disruptions.

Explanation:

• --cluster-name cluster_name: Marks the cluster to be updated, ensuring the correct application of configuration changes.
• --store-backend store_backend: Specifies the backend type; maintaining consistency is vital for applying changes successfully.
• --store-endpoints store_endpoints: Provides the path to the backend, ensuring proper delivery and application of the update payload.
• --patch 'cluster_spec': Details the JSON patch with the specific updates to be applied, enabling precise modification of the cluster specifications.

Example Output:

Update successful
New Specification:
Replicas: 2

Conclusion:

The stolonctl command-line interface is an invaluable tool for PostgreSQL administrators to ensure their database clusters remain highly available and easily manageable. Through targeted commands, administrators can verify cluster status, access detailed configurations, and make necessary updates to adapt to evolving requirements seamlessly. By effectively leveraging these capabilities, organizations can maintain the performance and reliability of their PostgreSQL clusters in a cloud-native environment.