conn_limit

conn_limit limits concurrent connections, in total and per client IP. Extra connections are closed immediately.

server:
  tcp:
    middlewares:
      limit:
        conn_limit:
          max: 1000
          max_per_ip: 20

Field	Default	Description
max	0	Maximum concurrent connections of the router, 0 is unlimited.
max_per_ip	0	Maximum concurrent connections of a client IP, 0 is unlimited.

At least one of the fields is required. A connection is counted until the rest of the chain returns, so place conn_limit before the terminal middleware (redirect, load_balancer...).