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TRIBE.md

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Tribe

Tribe is the name of the clustering feature in Snap. When it is enabled, snapd instances can join to one another through an agreement. When an action is taken by one snapd instance that is a member of an agreement, that action will be carried out by all other members of the agreement. When a new snapd joins an existing agreement it will retrieve plugins and tasks from the members of the agreement.

Usage

This walkthrough assumes you have downloaded a Snap release as described in Getting Started.

Starting the first snapd in tribe mode

Start the first node:

$ snapd --tribe -t 0

Only --tribe and some trust level (-t 0) is required to start tribe. This will result in defaults for all other parameters:

  • Default tribe-node-name will be the same as your hostname
  • Default tribe-seed is port 6000
  • Default tribe-addr and tribe-port are the same as snapd and tribe-seed (ex. 127.0.0.1:6000)

See snapd -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:

$ snapctl agreement create all-nodes
Name 	    Number of Members 	 plugins 	 tasks
all-nodes 	0 			         0 		     0

Join our running snapd into this agreement:

$ snapctl agreement join all-nodes `hostname`
Name 	    Number of Members 	 plugins 	 tasks
all-nodes 	1 			         0   		 0

Joining other snapd 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 snapd 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:

$ snapd --tribe -t 0 --tribe-port 6001 --api-port 8182 --tribe-node-name secondnodename --tribe-seed 192.168.136.176:6000

Both snapd instances will see each other in their member list:

$ snapctl member list
Name
secondnodename
firstnode

This member needs to join the agreement:

$ snapctl 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.

Examples

Starting a 4 node cluster and listing members tribe-start-list-members

Note: Once the cluster is started subsequent new nodes can choose to establish membership through any node as there is no "master".

Creating an agreement and joining members to it tribe-create-join-agreement

In the example below an agreement has been created and all members of the cluster have joined it. After loading a collector and publishing plugin and starting a task on one node we demonstrate that the plugins and tasks are now running on all of the other nodes in the agreement.

Loading plugins and starting a task on a node participating in an agreement tribe-load-start