Multi Data Center Deployments

Multinode clusters can be deployed in both Active/Active or Active/Standby configurations. Active/Active configurations have all the Unified nodes enabled for transaction processing. Active/Standby configurations have only the Unified nodes in the primary data center (the data center containing the Unified node with the primary database) enabled for transaction processing.

In order to run an Active/Active configuration, the latency (RTT) between data centers must not exceed 20ms. For higher latencies an Active/Standby configuration must be used.

To switch to an Active/Standby configuration, do the following on all Unified nodes in the secondary data center (the data center not containing the Unified node with the primary database):

  1. log into platform:

    ssh platform@<ip_address>

  2. set the worker count on the nodes in the secondary data center to zero:

    voss workers 0

    Setting the number of workers is persistent; in other words, this setting will still apply after upgrades and system restart.

For an Active/Standby configuration, the proxy server web weights should be set to the Unified nodes on the primary data center. This is done with the web weight add command.

The web weight specifies the routing and relative counts of the initial HTTP request from the Web Proxy to a Unified Node. The initial request could be a request such as a transaction, or for example a GET request. Consider web weights configuration as shown below:

172.0.0.158:443: 1
172.0.0.159:443: 1
172.0.0.161:443: 1
172.0.0.162:443: 1
173.0.0.163:443: 0
173.0.0.164:443: 0

This configuration means that the servers 173.0.0.163 and 173.0.0.164 serve as backup servers and requests are only routed to these if the other servers are not available. While the other servers are available, an equal number of requests are routed to them in a round-robin manner. Refer to the Best Practices Guide for more details on deployment models and web weight settings.

Consider an example where:

  1. Primary data center has unified nodes with IP addresses and ports:
    • 172.0.0.158:443
    • 172.0.0.159:443
    • 172.0.0.161:443
    • 172.0.0.162:443
  2. Secondary data center has unified nodes with IP addresses and ports:
    • 173.0.0.163:443
    • 173.0.0.164:443

The defaults of the web weight list command run on the proxy servers is as below:

  1. Primary data center proxy server:
$ web weight list
Default service weights
    upstreamservers:
        selfservice:
            172.0.0.158:443: 1
            172.0.0.159:443: 1
            172.0.0.161:443: 1
            172.0.0.162:443: 1
            173.0.0.163:443: 0
            173.0.0.164:443: 0
        voss-deviceapi:
            172.0.0.158:443: 1
            172.0.0.159:443: 1
            172.0.0.161:443: 1
            172.0.0.162:443: 1
            173.0.0.163:443: 0
            173.0.0.164:443: 0
  1. Secondary data center proxy server:
$ web weight list
Default service weights
    upstreamservers:
        selfservice:
            172.0.0.158:443: 0
            172.0.0.159:443: 0
            172.0.0.161:443: 0
            172.0.0.162:443: 0
            173.0.0.163:443: 1
            173.0.0.164:443: 1
        voss-deviceapi:
            172.0.0.158:443: 0
            172.0.0.159:443: 0
            172.0.0.161:443: 0
            172.0.0.162:443: 0
            173.0.0.163:443: 1
            173.0.0.164:443: 1

In order to ensure that the secondary data center is configured for a Standby mode, change the web weights to show userweights as seen in the output on the secondary data center proxy server below:

$ web weight list
Default service weights
    upstreamservers:
        selfservice:
            172.0.0.158:443: 0
            172.0.0.159:443: 0
            172.0.0.161:443: 0
            172.0.0.162:443: 0
            173.0.0.163:443: 1
            173.0.0.164:443: 1
        voss-deviceapi:
            172.0.0.158:443: 0
            172.0.0.159:443: 0
            172.0.0.161:443: 0
            172.0.0.162:443: 0
            173.0.0.163:443: 1
            173.0.0.164:443: 1

Customized service weights
    userweights:
        172.0.0.158:443: 1
        172.0.0.159:443: 1
        172.0.0.161:443: 1
        172.0.0.162:443: 1
        173.0.0.163:443: 0
        173.0.0.164:443: 0

As can be seen, the load balancing web weights have been changed to the unified nodes on the primary data center.