fix: Limit HAProxy maximum concurrent connections

If the limit is not configured, HAProxy derives it from the file
descriptor limit. The higher the limit, the more memory HAProxy
allocates. That limit can be so high on modern Linux distros that
HAproxy allocates all available memory.

images/haproxy/haproxy.cfg

@@ -14,6 +14,10 @@
 
 # minimal config file to avoid haproxy exiting due to invalid / missing config
 # kind will rewrite this config at runtime
+global
+    # limit memory usage to approximately 18 MB
+    maxconn 100000
+
 frontend controlPlane
     bind 0.0.0.0:6443
     mode tcp

pkg/cluster/internal/loadbalancer/config.go

@@ -36,6 +36,8 @@ global
   log /dev/log local0
   log /dev/log local1 notice
   daemon
+  # limit memory usage to approximately 18 MB
+  maxconn 100000
 
 resolvers docker
   nameserver dns 127.0.0.11:53