Load Balancer for Postgres

[nitishukg]

Hi, 

I have 2-3 read replica server in CloudSQL(Postgres) how should I configure the load balancing on those replica server? and which GCP service should i use for this??

[ms4446]

The recommended solution for load balancing read replicas in Cloud SQL for PostgreSQL is to use an external load balancer such as HAProxy. Cloud SQL does not provide built-in load balancing for read replicas, but HAProxy can be used to distribute read requests among your read replicas evenly and efficiently.

To use HAProxy for load balancing read replicas in Cloud SQL for PostgreSQL, you will need to:

1. Set up an HAProxy instance.
2. Configure HAProxy to distribute traffic to your Cloud SQL read replicas.
3. Update your application's connection string to point to the HAProxy instance's IP address and port.

Here is a brief overview of each step:

1. Set up an HAProxy instance:

You can deploy HAProxy on a variety of platforms, including on-premises servers, cloud VMs, and Kubernetes clusters. Once you have deployed HAProxy, you will need to configure it to listen on a specific port, such as 5432.

2. Configure HAProxy to distribute traffic to your Cloud SQL read replicas:

The HAProxy configuration will need to have the IP addresses of your Cloud SQL read replicas. You can use a variety of HAProxy load balancing algorithms, such as round-robin, weighted round-robin, and least connections. You can also use HAProxy's health checking features to monitor the health of your read replicas and redirect traffic away from any unhealthy replicas.

3. Update your application's connection string to point to the HAProxy instance's IP address and port:

Once you have configured HAProxy, you will need to update your application's connection string to point to the HAProxy instance's IP address and port. This will ensure that your application routes read requests to HAProxy, which will then distribute them to your Cloud SQL read replicas.

Here are some additional tips for using HAProxy to load balance read replicas in Cloud SQL for PostgreSQL:

• Use a highly available HAProxy deployment topology. You can deploy multiple HAProxy instances behind a load balancer to ensure that there is no single point of failure.
• Use HAProxy's health checking features to monitor the health of your Cloud SQL read replicas and redirect traffic away from any unhealthy replicas.
• Secure your HAProxy instance and only allow necessary traffic.
• Secure the communication between HAProxy and Cloud SQL.

Comparison of HAProxy and Cloud Load Balancing (TCP) for load balancing read replicas in Cloud SQL for PostgreSQL:

Feature	HAProxy	Cloud Load Balancing (TCP)
Cost	Open source and freely available	Pay-as-you-go
Managed service	No	Yes
Deployment complexity	More complex	Less complex
Features	Rich set of features, including weighted round-robin, least connections, and health checking	Basic set of features, but covers the most common needs

Conclusion:

Using HAProxy to load balance read replicas in Cloud SQL for PostgreSQL is a good option if you are looking for a cost-effective and highly customizable solution. However, it is important to note that HAProxy requires more manual configuration and management than a managed load balancing service such as Cloud Load Balancing (TCP).

[jay_hat]

I'm surprised to see HAProxy as the first option in many of these online threads.

At least for clients that use JDBC, they should start with this:

jdbc:postgresql://node1,node2,node3/accounting?targetServerType=preferSecondary&loadBalanceHosts=true

From postgres documentation: "And the read pool balances connections between secondary nodes, but allows connections also to a primary if no secondaries are available"

[nitishukg]

Hi @ms4446 ,

I tried the GCP Load Balancer but its only showing me to attach a instance group or a instance? but not finding any way to connect a CloudSQL instance? can you tell me exactly which GCP service to use?

[ms4446 · Accepted solution]

Hi @nitishukg,

To clarify, Google Cloud Platform's Cloud Load Balancing is designed to distribute incoming application traffic across multiple VM instances and does not natively support Cloud SQL instances. Therefore, you cannot use Cloud Load Balancing to directly load balance read replicas in Cloud SQL for PostgreSQL.

If you're looking to load balance read replicas for Cloud SQL, you'll need to use an external solution, such as HAProxy. Here's a brief overview:

1. Set Up HAProxy on a Compute Engine VM: Deploy an HAProxy instance on a Google Compute Engine VM. This instance will act as the load balancer for your Cloud SQL read replicas.

2. Configure HAProxy: Update the HAProxy configuration to include the IP addresses of your Cloud SQL read replicas. You can set up various load balancing algorithms, such as round-robin or least connections, to distribute the incoming read requests among the replicas.

3. Update Application Connection String: Point your application to the HAProxy instance's IP address and port. This ensures that your application's read requests are routed through HAProxy, which then distributes them to the Cloud SQL read replicas.

4. Security and Monitoring: Ensure that the communication between HAProxy and Cloud SQL is secure. Also, set up monitoring and health checks for the HAProxy instance to ensure smooth operation.

In summary, while GCP's native load balancers do not directly support Cloud SQL instances, you can achieve load balancing for Cloud SQL read replicas by setting up an external solution like HAProxy on a Compute Engine VM.

[nitishukg]

Thank you @ms4446  😀