Add load-balancing reverse-proxy documentation and examples

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+
+.. _load-balancing:
+
+#############
+Reverse-proxy
+#############
+.. include:: /_include/need_improvement.txt
+
+VyOS reverse-proxy is balancer and proxy server that provides
+high-availability, load balancing and proxying for TCP (level 4)
+and HTTP-based (level 7) applications.
+
+Configuration
+=============
+
+
+Service configuration is responsible for binding to a specific port,
+while the backend configuration determines the type of load balancing
+to be applied and specifies the real servers to be utilized.
+
+Service
+-------
+
+.. cfgcmd:: set load-balancing reverse-proxy service <name> listen-address
+   <address>
+
+  Set service to bind on IP address, by default listen on any IPv4 and IPv6
+
+.. cfgcmd:: set load-balancing reverse-proxy service <name> port
+   <port>
+
+  Create service `<name>` to listen on <port>
+
+.. cfgcmd:: set load-balancing reverse-proxy service <name> mode
+   <tcp|http>
+
+  Configure service `<name>` mode TCP or HTTP
+
+.. cfgcmd:: set load-balancing reverse-proxy service <name> backend
+   <name>
+
+  Configure service `<name>` to use the backend <name>
+
+.. cfgcmd:: set load-balancing reverse-proxy service <name> ssl
+   certificate <name>
+
+  Set SSL certeficate <name> for service <name>
+
+
+Rules
+^^^^^
+Rules allow to control and route incoming traffic to specific backend based
+on predefined conditions. Rules allow to define matching criteria and
+perform action accordingly.
+
+.. cfgcmd:: set load-balancing reverse-proxy service <name> rule <rule>
+   domain-name <name>
+
+  Match domain name
+
+.. cfgcmd:: set load-balancing reverse-proxy service <name> rule <rule>
+   ssl <sni>
+
+  SSL match Server Name Indication (SNI) option:
+   * ``req-ssl-sni`` SSL Server Name Indication (SNI) request match
+   * ``ssl-fc-sni`` SSL frontend connection Server Name Indication match
+   * ``ssl-fc-sni-end`` SSL frontend match end of connection Server Name 
+   Indication
+
+.. cfgcmd:: set load-balancing reverse-proxy service <name> rule <rule>
+   url-path <match> <url>
+
+  Allows to define URL path matching rules for a specific service.
+
+  With this command, you can specify how the URL path should be matched 
+  against incoming requests.
+
+  The available options for <match> are:
+   * ``begin`` Matches the beginning of the URL path
+   * ``end`` Matches the end of the URL path.
+   * ``exact`` Requires an exactly match of the URL path
+
+.. cfgcmd:: set load-balancing reverse-proxy service <name> rule <rule>
+   set backend <name>
+
+  Assign a specific backend to a rule
+
+.. cfgcmd:: set load-balancing reverse-proxy service <name> rule <rule>
+   redirect-location <url>
+
+  Redirect URL to a new location
+
+
+Backend
+-------
+
+.. cfgcmd:: set load-balancing reverse-proxy backend <name> balance
+   <balance>
+
+  Load-balancing algorithms to be used for distributind requests among the
+  vailable servers
+
+  Balance algorithms:
+   * ``source-address`` Distributes requests based on the source IP address
+     of the client
+   * ``round-robin`` Distributes requests in a circular manner,
+     sequentially sending each request to the next server in line
+   * ``least-connection`` Distributes requests tp tje server wotj the fewest 
+     active connections
+
+.. cfgcmd:: set load-balancing reverse-proxy backend <name> mode
+   <mode>
+
+  Configure backend `<name>` mode TCP or HTTP
+
+.. cfgcmd:: set load-balancing reverse-proxy backend <name> parameters
+   http-check
+
+  Enable layer 7 HTTP health check
+
+.. cfgcmd:: set load-balancing reverse-proxy backend <name> server
+   <name> address <x.x.x.x>
+
+  Set the address of the backend server to which the incoming traffic will
+  be forwarded
+
+.. cfgcmd:: set load-balancing reverse-proxy backend <name> server
+   <name> port <port>
+
+  Set the address of the backend port
+
+.. cfgcmd:: set load-balancing reverse-proxy backend <name> server
+   <name> check
+
+  Active health check backend server
+
+.. cfgcmd:: set load-balancing reverse-proxy backend <name> server
+   <name> send-proxy
+
+  Send a Proxy Protocol version 1 header (text format)
+
+.. cfgcmd:: set load-balancing reverse-proxy backend <name> server
+   <name> send-proxy-v2
+
+  Send a Proxy Protocol version 2 header (binary format)
+
+
+
+Gloabal
+-------
+
+Global parameters
+
+.. cfgcmd:: set load-balancing reverse-proxy global-parameters max-connections
+   <num>
+
+  Limit maximum number of connections
+
+.. cfgcmd:: set load-balancing reverse-proxy global-parameters ssl-bind-ciphers
+   <ciphers>
+
+  Limit allowed cipher algorithms used during SSL/TLS handshake
+
+.. cfgcmd:: set load-balancing reverse-proxy global-parameters tls-version-min
+   <version>
+
+  Specify the minimum required TLS version 1.2 or 1.3
+
+
+Redirect HTTP to HTTPS
+======================
+Configure the load-balancing reverse-proxy service for HTTP.
+
+This configuration listen on port 80 and redirect incoming
+requests to HTTPS:
+
+.. code-block:: none
+
+    set load-balancing reverse-proxy service http port '80'
+    set load-balancing reverse-proxy service http redirect-http-to-https
+
+The name of the service can be different, in this example it is only for 
+convenience.
+
+
+Examples
+========
+
+Level 4 balancing
+-----------------
+
+This configuration enables the TCP reverse proxy for the "my-tcp-api" service.
+Incoming TCP connections on port 8888 will be load balanced across the backend
+servers (srv01 and srv02) using the round-robin load-balancing algorithm.
+
+.. code-block:: none
+
+    set load-balancing reverse-proxy service my-tcp-api backend 'bk-01'
+    set load-balancing reverse-proxy service my-tcp-api mode 'tcp'
+    set load-balancing reverse-proxy service my-tcp-api port '8888'
+
+    set load-balancing reverse-proxy backend bk-01 balance 'round-robin'
+    set load-balancing reverse-proxy backend bk-01 mode 'tcp'
+
+    set load-balancing reverse-proxy backend bk-01 server srv01 address '192.0.2.11'
+    set load-balancing reverse-proxy backend bk-01 server srv01 port '8881'
+    set load-balancing reverse-proxy backend bk-01 server srv02 address '192.0.2.12'
+    set load-balancing reverse-proxy backend bk-01 server srv02 port '8882'
+
+Balancing based on domain name
+------------------------------
+The following configuration demonstrates how to use VyOS
+to achieve load balancing based on the domain name.
+
+The HTTP service listen on TCP port 80.
+
+Rule 10 matches requests with the domain name ``node1.example.com`` forwards
+to the backend ``bk-api-01``
+
+Rule 20 matches requests with the domain name ``node2.example.com`` forwards
+to the backend ``bk-api-02``
+
+.. code-block:: none
+
+    set load-balancing reverse-proxy service http description 'bind app listen on 443 port'
+    set load-balancing reverse-proxy service http mode 'tcp'
+    set load-balancing reverse-proxy service http port '80'
+
+    set load-balancing reverse-proxy service http rule 10 domain-name 'node1.example.com'
+    set load-balancing reverse-proxy service http rule 10 set backend 'bk-api-01'
+    set load-balancing reverse-proxy service http rule 20 domain-name 'node2.example.com'
+    set load-balancing reverse-proxy service http rule 20 set backend 'bk-api-02'
+
+    set load-balancing reverse-proxy backend bk-api-01 description 'My API-1'
+    set load-balancing reverse-proxy backend bk-api-01 mode 'tcp'
+    set load-balancing reverse-proxy backend bk-api-01 server api01 address '127.0.0.1'
+    set load-balancing reverse-proxy backend bk-api-01 server api01 port '4431'
+    set load-balancing reverse-proxy backend bk-api-02 description 'My API-2'
+    set load-balancing reverse-proxy backend bk-api-02 mode 'tcp'
+    set load-balancing reverse-proxy backend bk-api-02 server api01 address '127.0.0.2'
+    set load-balancing reverse-proxy backend bk-api-02 server api01 port '4432'
+
+
+Terminate SSL
+-------------
+The following configuration reverse-proxy terminate SSL.
+
+The ``http`` service is lestens on port 80 and force redirects from HTTP to
+HTTPS.
+
+The ``https`` service listens on port 443 with backend `bk-default` to 
+handle HTTPS traffic. It uses certificate named ``cert`` for SSL termination.
+
+Rule 10 matches requests with the exact URL path ``/.well-known/xxx``
+and redirects to location ``/certs/``.
+
+Rule 20 matches requests with URL paths ending in ``/mail`` or exact
+path ``/email/bar`` redirect to location ``/postfix/``.
+
+Additional global parameters are set, including the maximum number
+connection limit of 4000 and a minimum TLS version of 1.3.
+
+
+.. code-block:: none
+
+    set load-balancing reverse-proxy service http description 'Force redirect to HTTPS'
+    set load-balancing reverse-proxy service http port '80'
+    set load-balancing reverse-proxy service http redirect-http-to-https
+
+    set load-balancing reverse-proxy service https backend 'bk-default'
+    set load-balancing reverse-proxy service https description 'listen on 443 port'
+    set load-balancing reverse-proxy service https mode 'http'
+    set load-balancing reverse-proxy service https port '443'
+    set load-balancing reverse-proxy service https ssl certificate 'cert'
+
+    set load-balancing reverse-proxy service https rule 10 url-path exact '/.well-known/xxx'
+    set load-balancing reverse-proxy service https rule 10 set redirect-location '/certs/'
+    set load-balancing reverse-proxy service https rule 20 url-path end '/mail'
+    set load-balancing reverse-proxy service https rule 20 url-path exact '/email/bar'
+    set load-balancing reverse-proxy service https rule 20 set redirect-location '/postfix/'
+
+    set load-balancing reverse-proxy backend bk-default description 'Default backend'
+    set load-balancing reverse-proxy backend bk-default mode 'http'
+    set load-balancing reverse-proxy backend bk-default server sr01 address '192.0.2.23'
+    set load-balancing reverse-proxy backend bk-default server sr01 port '80'
+
+    set load-balancing reverse-proxy global-parameters max-connections '4000'
+    set load-balancing reverse-proxy global-parameters tls-version-min '1.3'
+