About Admin Processes and Peering

The role of an admin process is to provide database life cycle control (start, stop) for database processes, that is transaction engines (TEs) and/or storage managers (SMs). An admin process provides the following:

Each admin process has a complete durable record, that is, a persistent copy on disk, of the entire domain, including all hosts, and all databases and their processes. A domain is functional only with at least one admin process. For continuous availability, each data center (and availability zone) should run at least one admin process.

Notes on Admin Processes and Peering

A domain must contain at least one admin process. Any additional admin processes join the domain by securely connecting (peering) into the domain by means of another admin process. The admin processes communicate by pinging each other to make sure they are still accessible and available.

In physical / VMware deployments, each admin process is configured to run on its own physical host in the domain. Post-installation, the admin process is not started by default.

The nuoadmin.conf file on each host must be configured appropriate for the intended deployment configuration. The settings of the initial membership and or peer property is the same in each of the nuoadmin.conf files on each host. On each host, the value of the peering property value used is the hostname and port of the host machine running the initial admin process.

The first admin process started (A1) becomes the quorum leader admin server. The leader admin server performs the liveliness checks for the domain peers and determines if another admin (peer) is no longer responding. After admin server A2 and A3 are started, they peer into the domain through A1.

All admin processes have a last known state for the domain, so they can be restarted in any order and will reconnect properly. The initial peer used to connect to the domain no longer matters.

A NuoDB domain can be expanded dynamically by starting additional admin processes on new hosts, and peering them into the domain. The incoming admin process only needs to connect to any existing admin processes in the domain by using the address and port of an existing admin process. Also, an admin process can be removed dynamically and gracefully from the domain using the shutdown server command .

Note: The shutdown server command is issued using NuoDB Command (nuocmd). For information on using NuoDB Command and other NuoDB command line utilities, see Command Line Tools.

In summary:

See also Creating the Domain and Adding Hosts.