There should be only a SMALL number of open file descriptors required for a Consul client agent. The gossip LAYERS perform transient connections with other NODES, each connection to the client agent (such as for a blocking query) will open a connection, and there will typically be connections to one of the Consul servers. A small number of file descriptors are also required for watch handlers, health checks, log files, and so on.

For a Consul server agent, you should plan on the above requirements and an additional incoming connection from each of the nodes in the cluster. This should not be the common case, but in the worst case if there is a problem with the other servers you would expect the other client agents to all connect to a single server and so preparation for this possibility is helpful.

The DEFAULT ulimits are usually sufficient for Consul, but you should closely scrutinize your own environment's specific needs and identify the root cause of any excessive resource UTILIZATION before arbitrarily increasing the limits.

There should be only a small number of open file descriptors required for a Consul client agent. The gossip layers perform transient connections with other nodes, each connection to the client agent (such as for a blocking query) will open a connection, and there will typically be connections to one of the Consul servers. A small number of file descriptors are also required for watch handlers, health checks, log files, and so on.

For a Consul server agent, you should plan on the above requirements and an additional incoming connection from each of the nodes in the cluster. This should not be the common case, but in the worst case if there is a problem with the other servers you would expect the other client agents to all connect to a single server and so preparation for this possibility is helpful.

The default ulimits are usually sufficient for Consul, but you should closely scrutinize your own environment's specific needs and identify the root cause of any excessive resource utilization before arbitrarily increasing the limits.