Tribe is the name of the clustering feature in Snap. When it is enabled, snapteld instances can join to one another through an
agreement. When an action is taken by one snapteld instance that is a member of an agreement, that action will be carried out by all other members of the agreement. When a new snapteld joins an existing agreement it will retrieve plugins and tasks from the members of the agreement.
This walkthrough assumes you have downloaded a Snap release as described in Getting Started.
Starting the first snapteld in tribe mode
Start the first node:
$ snapteld --tribe -t 0
--tribe and some trust level (
-t 0) is required to start tribe. This will result in defaults for all other parameters:
tribe-node-namewill be the same as your hostname
tribe-seedis port 6000
tribe-portare the same as
snapteld -h for all the possible flags.
Creating an initial agreement
Members of a tribe only share configuration once they join an agreement. To create your first agreement:
$ snaptel agreement create all-nodes Name Number of Members plugins tasks all-nodes 0 0 0
Join our running snapteld into this agreement:
$ snaptel agreement join all-nodes `hostname` Name Number of Members plugins tasks all-nodes 1 0 0
Joining other snapteld into an existing tribe
Since tribe is implemented on top of a gossip based protocol there is no "master." All other nodes who join a tribe by communicating with any existing member.
Start another instance of snapteld to join to our existing tribe. The local IP address is 192.168.136.176 in our example. Note that we need a few more parameters to avoid conflicting ports on a single system:
$ snapteld --tribe -t 0 --tribe-port 6001 --api-port 8182 --tribe-node-name secondnodename --tribe-seed 192.168.136.176:6000 --control-listen-port 8083
Both snapteld instances will see each other in their member list:
$ snaptel member list Name secondnodename firstnode
This member needs to join the agreement:
$ snaptel agreement join all-nodes secondnodename Name Number of Members plugins tasks all-nodes 2 0 0
From this point forward, any plugins or tasks you load will load into both members of this agreement.
Note: Once the cluster is started subsequent new nodes can choose to establish membership through any node as there is no "master".