Deploying openLooKeng with High Availability(HA)

The openLooKeng HA solves single point failure of coordinators. Users can submit queries to any coordinator to balance the workloads.

Installing HA

openLooKeng with HA is required to be installed with minimum of 2 coordinators in the cluster. Make sure the time on all coordinators have been sync up. Please follow Deploying openLooKeng Manually or Deploying openLooKeng Automatically for basic installation.

Configuring HA

###Configuring Coordinator and Worker Add following configuration to etc/config.properties on all coordinators.

hetu.multiple-coordinator.enabled=true
hetu.embedded-state-store.enabled=true  

Add following configuration to etc/config.properties on all workers.

hetu.multiple-coordinator.enabled=true

The above properties are described below:

  • hetu.multiple-coordinator.enabled: Enable multiple coordinators.
  • hetu.embedded-state-store.enabled: Enable coordinators to start embedded state store.

Note: It is suggested to enable embedded state store on all coordinators(or at least 3) to guarantee the high availability of service when node/network is down.

###Configuring State Store Please refer to the section State Store to configure state store.

HA Cluster behind Reverse Proxy

To achieve the full benefit of HA, clients(ie. openLooKeng CLI, JDBC, etc) are encouraged to not connect to specific coordinators directly. Instead, they should connect to multiple coordinators through some sort of reverse proxy, for example through a load balancer, or a Kubernetes service. This allows the client to continue to work even if a specific coordinator is not working as expected.

Reverse Proxy Requirement

When the connection is made through a reverse proxy, it is required for a given client to connect to the same coordinator during the execution of a query. This is to ensure a constant heartbeat between the client and coordinator while that query is running. This can be achieved by enabling sticky connections, for example, Nginx’s ip_hash.

Configure Reverse Proxy Example (Nginx)

Please include configuration below in the Nginx configuration file (ie. nginx.conf).

http {
    ...  # Your own configuration
    upstream backend {
        ip_hash;
        server <coordinator1_ip>:<coordinator1_port>;
        server <coordinator2_ip>:<coordinator2_port>;
        server <coordinator3_ip>:<coordinator3_port>;
        ...
    }

    server {
        ... # Your own configuration
        location / {
            proxy_pass http://backend;
            proxy_set_header Host <nginx_ip>:<nginx_port>;
        }
    }
}