haproxy: Remove detailed config, since it is not applicable for CE single server

Author: slusarz

docs/core/config/proxy/haproxy.md

@@ -14,65 +14,14 @@ dovecotlinks:
 open source software "TCP and HTTP" Load Balancer and proxying solution.
 It is available as a package on almost all Linux distros.
 
-::: tip
-HAProxy is the recommended way to do software load balancing for Dovecot.
+::: warning
+Dovecot CE supports single-server operation only, so load balancing is not
+applicable.
 
-This page is not intended to be a comprehensive HAProxy manual; it is designed
-to broadly explain how HAProxy can be used in a Dovecot-specific environment.
+This page exists to document HAProxy-related features that exist in the
+software.
 :::
 
-The configuration is located at `/etc/haproxy/haproxy.cfg`.
-
-## Frontends
-
-A frontend defines how requests should be forwarded to backends. Frontends
-are defined in the frontend section of the HAProxy configuration. Their
-definitions are composed of the following components:
-
-* A set of IP addresses and a port (e.g. `10.10.10.1, *:443`)
-* ACLs
-* `use_backend` rules, which define which backends to use depending on
-  which ACL conditions are matched, and/or a `default_backend` rule that
-  handles every other case.
-
-An example of a front-end:
-
-```
-frontend front_dc_pop3
-    bind             :1110
-    mode             tcp
-    default_backend  back_dc_pop3
-```
-
-This configures a frontend named `front_dc_pop3`, which handles all
-incoming traffic on port 1110. This will send all traffic to the backends
-defined by `back_dc_pop3`.
-
-## Access Control Lists (ACL)
-
-In relation to load balancing, ACLs are used to test some condition and
-perform an action (e.g. select a server, or block a request) based on the
-test result. 
-
-This is similar in concept to an if-else snippet where execution takes
-place based upon the success or failure of a particular block. Use of ACLs
-allows flexible network traffic forwarding based on a variety of factors
-like pattern-matching and the number of connections to a backend.
-
-Example of an ACL:
-
-```
-acl url_stats path_beg /stats
-```
-
-This ACL is matched if the path of a request begins with `/stats`. This
-would match a request of http://10.10.10.1/stats, for example.
-
-Here, `url_stats` is just the label given to the pattern.
-
-For more details on ACLs please refer to the official
-[HAProxy documentation](https://www.haproxy.org/).
-
 ## TLS Forwarding
 
 For Dovecot to recognize that TLS termination has been performed, you need to
@@ -85,111 +34,3 @@ server s1 127.0.0.1:143 send-proxy-v2-ssl
 ```
 
 See also: [[link,secured_connections]].
-
-## Backends
-
-A backend is a set of servers that receives forwarded requests.
-
-Backends are defined in the backend section of the HAProxy configuration. In
-its most basic form, a backend can be defined by:
-
-* Which load balance algorithm to use (mentioned below)
-* A list of servers and ports
-
-A backend can contain one or many servers. Adding more servers to your
-backend will generally increase the both the reliability and load capacity
-of the configured service by distributing the load over multiple servers. 
-
-Here is an example of a two backend configurations, `back_dc_pop3` and
-`back_dc_lmtp`, with two servers in each, listening for `pop3` and `lmtp`
-traffic respectively:
-
-```
-backend back_dc_pop3
-    mode     tcp
-    balance  leastconn
-    option   allbackups
-    server   10.41.1.131 10.41.1.131:110 check inter 5s
-    server   10.41.1.116 10.41.1.116:110 check inter 5s
- 
-backend back_dc_lmtp
-    mode     tcp
-    balance  leastconn
-    option   allbackups
-    server   10.41.1.131 10.41.1.131:24 check inter 5s
-    server   10.41.1.116 10.41.1.116:24 check inter 5s
-```
-
-::: info
-Details about load balancing methods and options are available in the
-haproxy documentation if you need more information.
-:::
-
-## Health Checking
-
-HAProxy uses health checks to determine if a backend server is available to
-process requests. This avoids having to manually remove a server from
-the backend if it becomes unavailable.
-
-The default health check is to try to establish a TCP connection to the
-server. E.g., it checks if the backend server is listening on the
-configured IP address and port.
-
-## Sample Configuration
-
-HAProxy configured between Dovecot Backends and Scality sproxyd:
-
-```
-global
-    log      127.0.0.1 local2
-    chroot   /var/lib/haproxy
-    pidfile  /var/run/haproxy.pid
-    maxconn  60000
-    user     haproxy
-    group    haproxy
-    daemon
-    stats    socket /var/lib/haproxy/stats
-   
-defaults
-   mode     http
-   log      global
-   option   httplog
-   option   dontlognull
-   option   http-server-close
-   option   forwardfor except 127.0.0.0/8
-   option   redispatch
-   retries                  3
-   timeout  http-request    1m
-   timeout  queue           1m
-   timeout  connect         10s
-   timeout  client          1m
-   timeout  server          1m
-   timeout  http-keep-alive 10m
-   timeout  check           10s
-   maxconn                  5000
-  
-frontend  scality_in
-    bind             :::81
-    option           forwardfor
-    option           httplog
-    default_backend  scality_ring
-  
-    # Capture X-Dovecot-Reason, X-Dovecot-Username and
-	# X-Dovecot-Session-Id headers
-    capture request header X-Dovecot-Reason len 40
-    capture request header X-Dovecot-Username len 40
-    capture request header X-Dovecot-Session-Id len 70
-  
-backend scality_ring
-    balance         roundrobin
-    mode            http
-    option          forwardfor
-    option          httpchk
-    default-server  inter 30s
-    server          10.10.10.1 10.10.10.1:81 check
-    server          10.10.10.2 10.10.10.2:81 check
-    server          10.10.10.3 10.10.10.3:81 check
-    server          10.10.10.4 10.10.10.4:81 check
-    server          10.10.10.5 10.10.10.5:81 check
-    server          10.10.10.6 10.10.10.6:81 check
-```