Docker Digs Multiple Vs Managers And Workers
I have a docker cluster node. Perhaps we will have 2 managers. I know that once there is only one leader. Since this is a 3 node cluster, I am trying to find some literature to understand what the pros and cons of multiple managers are. I need this information since my cluster has 3 node, if I have 2 masters, 1 worker, which is a disadvantage if I just create 3 masters in the cluster. Any thoughts would be helpful.
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Dockers with two managers are not recommended .
Why?
Docker swarm implements the RAFT consensus :
The raft tolerates up to (N-1) / 2 failures and requires a majority or quorum (N / 2) +1 members to reconcile the values proposed to the cluster. This means that in a cluster of 5 managers running Raft, if 3 nodes are unavailable, the system will not process any more requests to schedule additional tasks.
Thus, with two managers, if one of them is disabled, the other will not be able to schedule additional tasks (without updating the cluster, without new services, etc.).
The docs also clearly state the number of managers you must have for high availability :
Deployment size
To make the cluster tolerant of more failures, add additional replica nodes to your cluster.
Manager nodes Failures tolerated 1 0 3 1 5 2 7 3
So, in a nutshell, as the doc says here :
Adding more managers does NOT mean increased scalability or better performance. In general, the opposite is true.
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