Add workers documentation.

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diff --git a/doc/markdown/workers/controller.md b/doc/markdown/workers/controller.md
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diff --git a/doc/markdown/workers/index.md b/doc/markdown/workers/index.md
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+# Rspamd workers
+
+Rspamd defines several types of worker processes. Each type is designed for its specific
+purpose, for example to scan mail messages, to perform control actions, such as learning or
+statistic grabbing. There is also flexible worker type named `lua` worker that allows
+to run any lua script as rspamd worker providing proxy from rspamd lua API.
+
+## Worker types
+
+Currently rspamd defines the following worker types:
+
+- [normal](normal.md): this worker is designed to scan mail messages
+- [controller](controller.md): this worker performs configuration actions, such as
+learning, adding fuzzy hashes and serving web interface requests
+- [fuzzy_storage](fuzzy_storage.md): stores fuzzy hashes
+- [lua](lua_worker.md): runs custom lua scripts
+
+## Workers connections
+
+All client applications should interact with two main workers: `normal` and `controller`.
+Both of these workers use `HTTP` protocol for all operations and rely on HTTP headers
+to get extra information from a client. Depending on network configuration, it might be
+useful to bind all workers to the loopback interface preventing all interaction from the
+outside. Rspamd workers are **not** supposed to run in an unprotected environment, such as
+Internet. Currently there is neither secrecy nor integrity control in these protocols and
+using of plain HTTP might leak sensitive information.
+
+[Fuzzy worker](fuzzy_storage.md) is different: it is intended to serve external requests, however, it
+listens on an UDP port and does not save any state information.
+
+## Common workers options
+
+All workers shares a set of common options. Here is a typical example of a normal
+worker configuration that uses merely common worker options:
+
+~~~nginx
+worker {
+    type = "normal";
+    bind_socket = "*:11333";
+}
+~~~
+
+Here are options available to all workers:
+
+- `type` - a **mandatory** string that defines type of worker.
+- `bind_socket` - a string that defines bind address of a worker.
+- `count` - number of worker instances to run (some workers ignore that option, e.g. `fuzzy_storage`)
+
+`bind_socket` is the mostly common used option. It defines the address where worker should accept
+connections. Rspamd allows both names and IP addresses for this option:
+
+~~~nginx
+bind_socket = "localhost:11333";
+bind_socket = "127.0.0.1:11333";
+bind_socket = "[::1]:11333"; # note that you need to enclose ipv6 in '[]'
+~~~
+
+Also universal listening addresses are defined:
+
+~~~nginx
+bind_socket = "*:11333"; # any ipv4 and ipv6 address
+bind_socket = "*v4:11333"; # any ipv4 address
+bind_socket = "*v6:11333"; # any ipv6 address
+~~~
+
+Moreover, you can specify systemd sockets if rspamd is invoked by systemd:
+
+~~~nginx
+bind_socket = "systemd:1"; # the first socket passed by systemd throught environment
+~~~
+
+You can specify multiple `bind_socket` options to listen on as many addresses as
+you want.
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diff --git a/doc/markdown/workers/lua_worker.md b/doc/markdown/workers/lua_worker.md
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diff --git a/doc/markdown/workers/normal.md b/doc/markdown/workers/normal.md
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