Add a new emqx image docs (#2032)

Signed-off-by: zhanghongtong <rory-z@outlook.com>

emqx/README-short.txt

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+An Open-Source, Cloud-Native, Distributed MQTT Message Broker for IoT.

emqx/content.md

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+# What is EMQ X ?
+
+[EMQ X MQTT broker](https://www.emqx.io/) is a fully open source, highly scalable, highly available distributed MQTT messaging broker for IoT, M2M and Mobile applications that can handle tens of millions of concurrent clients.
+
+Starting from 3.0 release, *EMQ X* broker fully supports MQTT V5.0 protocol specifications and backward compatible with MQTT V3.1 and V3.1.1, as well as other communication protocols such as MQTT-SN, CoAP, LwM2M, WebSocket and STOMP. The 3.0 release of the *EMQ X* broker can scaled to 10+ million concurrent MQTT connections on one cluster.
+
+%%LOGO%%
+
+# How to use this image
+
+### Run emqx
+
+Execute some command under this docker image
+
+```console
+$ docker run -d --name emqx %%IMAGE%%:tag
+```
+
+For example
+
+```console
+$ docker run -d --name emqx -p 18083:18083 -p 1883:1883 %%IMAGE%%:latest
+```
+
+The emqx broker runs as linux user `emqx` in the docker container.
+
+### Configuration
+
+Use the environment variable to configure the EMQ X docker container.
+
+By default, the environment variables with `EMQX_` prefix are mapped to key-value pairs in configuration files.
+
+You can change the prefix by overriding `HOCON_ENV_OVERRIDE_PREFIX`.
+
+Example:
+
+```bash
+EMQX_LISTENERS__SSL__DEFAULT__ACCEPTORS <--> listeners.ssl.default.acceptors
+EMQX_ZONES__DEFAULT__MQTT__MAX_PACKET_SIZE <--> zones.default.mqtt.max_packet_size
+```
+
+-	Prefix `EMQX_` is removed
+-	All upper case letters is replaced with lower case letters
+-	`__` is replaced with `.`
+
+If `HOCON_ENV_OVERRIDE_PREFIX=DEV_` is set:
+
+```bash
+DEV_LISTENER__SSL__EXTERNAL__ACCEPTORS <--> listener.ssl.external.acceptors
+DEV_MQTT__MAX_PACKET_SIZE              <--> mqtt.max_packet_size
+```
+
+Non mapped environment variables:
+
+```bash
+EMQX_NAME
+EMQX_HOST
+```
+
+These environment variables will ignore for configuration file.
+
+#### EMQ X Configuration
+
+> NOTE: All EMQ X Configuration in [etc/emqx.conf](https://github.com/emqx/emqx/blob/master/etc/emqx.conf) could config by environment. The following list is just an example, not a complete configuration.
+
+| Options     | Default        | Mapped | Description                |
+|-------------|----------------|--------|----------------------------|
+| `EMQX_NAME` | container name | none   | emqx node short name       |
+| `EMQX_HOST` | container IP   | none   | emqx node host, IP or FQDN |
+
+The list is incomplete and may changed with [etc/emqx.conf](https://github.com/emqx/emqx/blob/master/etc/emqx.conf) and plugin configuration files. But the mapping rule is similar.
+
+If set `EMQX_NAME` and `EMQX_HOST`, and unset `EMQX_NODE_NAME`, `EMQX_NODE_NAME=$EMQX_NAME@$EMQX_HOST`.
+
+For example, set mqtt tcp port to 1883
+
+```console
+$ docker run -d --name emqx -e EMQX__LISTENERS__TCP__DEFAULT__BIND=1883 -p 18083:18083 -p 1883:1883 %%IMAGE%%:latest
+```
+
+#### EMQ Loaded Modules Configuration
+
+| Options               | Default           | Description                 |
+|-----------------------|-------------------|-----------------------------|
+| `EMQX_LOADED_MODULES` | see content below | default modules emqx loaded |
+
+Default environment variable `EMQX_LOADED_MODULES`, including
+
+-	`emqx_mod_presence`
+
+```bash
+# The default EMQX_LOADED_MODULES env
+EMQX_LOADED_MODULES="emqx_mod_presence"
+```
+
+For example, set `EMQX_LOADED_MODULES=emqx_mod_delayed,emqx_mod_rewrite` to load these two modules.
+
+You can use comma, space or other separator that you want.
+
+All the modules defined in env `EMQX_LOADED_MODULES` will be loaded.
+
+```bash
+EMQX_LOADED_MODULES="emqx_mod_delayed,emqx_mod_rewrite"
+EMQX_LOADED_MODULES="emqx_mod_delayed emqx_mod_rewrite"
+EMQX_LOADED_MODULES="emqx_mod_delayed | emqx_mod_rewrite"
+```
+
+#### EMQ Loaded Plugins Configuration
+
+| Options               | Default           | Description                 |
+|-----------------------|-------------------|-----------------------------|
+| `EMQX_LOADED_PLUGINS` | see content below | default plugins emqx loaded |
+
+Default environment variable `EMQX_LOADED_PLUGINS`, including
+
+-	`emqx_recon`
+-	`emqx_retainer`
+-	`emqx_rule_engine`
+-	`emqx_management`
+-	`emqx_dashboard`
+
+```bash
+# The default EMQX_LOADED_PLUGINS env
+EMQX_LOADED_PLUGINS="emqx_recon,emqx_retainer,emqx_management,emqx_dashboard"
+```
+
+For example, set `EMQX_LOADED_PLUGINS= emqx_retainer,emqx_rule_engine` to load these two plugins.
+
+You can use comma, space or other separator that you want.
+
+All the plugins defined in `EMQX_LOADED_PLUGINS` will be loaded.
+
+```bash
+EMQX_LOADED_PLUGINS="emqx_retainer,emqx_rule_engine"
+EMQX_LOADED_PLUGINS="emqx_retainer emqx_rule_engine"
+EMQX_LOADED_PLUGINS="emqx_retainer | emqx_rule_engine"
+```
+
+#### EMQ X Plugins Configuration
+
+The environment variables which with `EMQX_` prefix are mapped to all emqx plugins' configuration file, `.` get replaced by `__`.
+
+Example:
+
+```bash
+EMQX_RETAINER__STORAGE_TYPE <--> retainer.storage_type
+EMQX_RETAINER__MAX_PAYLOAD_SIZE <--> retainer.max_payload_size
+```
+
+Don't worry about where to find the configuration file of emqx plugins, this docker image will find and config them automatically using some magic.
+
+All plugin of emqx project could config in this way, following the environment variables mapping rule above.
+
+Assume you are using redis auth plugin, for example:
+
+```bash
+#EMQX_RETAINER__STORAGE_TYPE = "ram"
+#EMQX_RETAINER.MAX_PAYLOAD_SIZE = 1MB
+
+docker run -d --name emqx -p 18083:18083 -p 1883:1883 -p 4369:4369 \
+    -e EMQX_LISTENERS__TCP__DEFAULT=1883 \
+    -e EMQX_LOADED_PLUGINS="emqx_retainer" \
+    -e EMQX_RETAINER__STORAGE_TYPE = "ram" \
+    -e EMQX_RETAINER__MAX_PAYLOAD_SIZE = 1MB \
+    %%IMAGE%%:latest
+```
+
+For numbered configuration options where the number is next to a `.` such as:
+
+-	backend.redis.pool1.server
+-	backend.redis.hook.message.publish.1
+
+You can configure an arbitrary number of them as long as each has a uniq unber for it's own configuration option:
+
+```bash
+docker run -d --name emqx -p 18083:18083 -p 1883:1883 -p 4369:4369 \
+    -e EMQX_BACKEND_REDIS_POOL1__SERVER=127.0.0.1:6379 \
+    [...]
+    -e EMQX_BACKEND__REDIS__POOL5__SERVER=127.0.0.5:6379 \
+    -e EMQX_BACKEND__REDIS__HOOK_MESSAGE__PUBLISH__1='{"topic": "persistant/topic1", "action": {"function": "on_message_publish"}, "pool": "pool1"}' \
+    -e EMQX_BACKEND__REDIS__HOOK_MESSAGE__PUBLISH__2='{"topic": "persistant/topic2", "action": {"function": "on_message_publish"}, "pool": "pool1"}' \
+    -e EMQX_BACKEND__REDIS__HOOK_MESSAGE__PUBLISH__3='{"topic": "persistant/topic3", "action": {"function": "on_message_publish"}, "pool": "pool1"}' \
+    [...]
+    -e EMQX_BACKEND__REDIS__HOOK_MESSAGE__PUBLISH__13='{"topic": "persistant/topic13", "action": {"function": "on_message_publish"}, "pool": "pool1"}' \
+    %%IMAGE%%:latest
+```
+
+### Cluster
+
+EMQ X supports a variety of clustering methods, see our [documentation](https://docs.emqx.io/broker/latest/en/advanced/cluster.html#emqx-service-discovery) for details.
+
+Let's create a static node list cluster from docker-compose.
+
+-	Create `docker-compose.yaml`:
+
+```yaml
+  version: '3'
+
+  services:
+    emqx1:
+      image: %%IMAGE%%:latest
+      environment:
+      - "EMQX_NAME=emqx"
+      - "EMQX_HOST=node1.emqx.io"
+      - "EMQX_CLUSTER__DISCOVERY_STRATEGY=static"
+      - "EMQX_CLUSTER__STATIC__SEEDS=[emqx@node1.emqx.io, emqx@node2.emqx.io]"
+      networks:
+        emqx-bridge:
+          aliases:
+          - node1.emqx.io
+
+    emqx2:
+      image: %%IMAGE%%:latest
+      environment:
+      - "EMQX_NAME=emqx"
+      - "EMQX_HOST=node2.emqx.io"
+      - "EMQX_CLUSTER__DISCOVERY_STRATEGY=static"
+      - "EMQX_CLUSTER__STATIC__SEEDS=[emqx@node1.emqx.io, emqx@node2.emqx.io]"
+      networks:
+        emqx-bridge:
+          aliases:
+          - node2.emqx.io
+
+  networks:
+    emqx-bridge:
+      driver: bridge
+```
+
+-	Start the docker-compose cluster
+
+```bash
+  docker-compose -p my_emqx up -d
+```
+
+-	View cluster
+
+```bash
+  $ docker exec -it my_emqx_emqx1_1 sh -c "emqx_ctl cluster status"
+  Cluster status: #{running_nodes => ['emqx@node1.emqx.io','emqx@node2.emqx.io'],
+                    stopped_nodes => []}
+```
+
+### Persistence
+
+If you want to persist the EMQ X docker container, you need to keep the following directories:
+
+-	`/opt/emqx/data`
+-	`/opt/emqx/etc`
+-	`/opt/emqx/log`
+
+Since data in these folders are partially stored under the `/opt/emqx/data/mnesia/${node_name}`, the user also needs to reuse the same node name to see the previous state. In detail, one needs to specify the two environment variables: `EMQX_NAME` and `EMQX_HOST`, `EMQX_HOST` set as `127.0.0.1` or network alias would be useful.
+
+In if you use docker-compose, the configuration would look something like this:
+
+```YAML
+volumes:
+  vol-emqx-data:
+    name: foo-emqx-data
+  vol-emqx-etc:
+    name: foo-emqx-etc
+  vol-emqx-log:
+    name: foo-emqx-log
+
+services:
+  emqx:
+    image: %%IMAGE%%:latest
+    restart: always
+    environment:
+      EMQX_NAME: foo_emqx
+      EMQX_HOST: 127.0.0.1
+    volumes:
+      - vol-emqx-data:/opt/emqx/data
+
+      - vol-emqx-log:/opt/emqx/log
+```
+
+### Kernel Tuning
+
+Under linux host machine, the easiest way is [Tuning guide](https://docs.emqx.io/en/broker/latest/tutorial/tune.html#linux-kernel-tuning).
+
+If you want tune linux kernel by docker, you must ensure your docker is latest version (>=1.12).
+
+```bash
+
+docker run -d --name emqx -p 18083:18083 -p 1883:1883 -p 4369:4369 \
+    --sysctl fs.file-max=2097152 \
+    --sysctl fs.nr_open=2097152 \
+    --sysctl net.core.somaxconn=32768 \
+    --sysctl net.ipv4.tcp_max_syn_backlog=16384 \
+    --sysctl net.core.netdev_max_backlog=16384 \
+    --sysctl net.ipv4.ip_local_port_range=1000 65535 \
+    --sysctl net.core.rmem_default=262144 \
+    --sysctl net.core.wmem_default=262144 \
+    --sysctl net.core.rmem_max=16777216 \
+    --sysctl net.core.wmem_max=16777216 \
+    --sysctl net.core.optmem_max=16777216 \
+    --sysctl net.ipv4.tcp_rmem=1024 4096 16777216 \
+    --sysctl net.ipv4.tcp_wmem=1024 4096 16777216 \
+    --sysctl net.ipv4.tcp_max_tw_buckets=1048576 \
+    --sysctl net.ipv4.tcp_fin_timeout=15 \
+    %%IMAGE%%:latest
+
+```
+
+> REMEMBER: DO NOT RUN EMQ X DOCKER PRIVILEGED OR MOUNT SYSTEM PROC IN CONTAINER TO TUNE LINUX KERNEL, IT IS UNSAFE.

emqx/get-help.md

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+[Discussions](https://github.com/emqx/emqx/discussions) or [Slack](https://slack-invite.emqx.io/)

emqx/github-repo

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+https://github.com/emqx/emqx-docker

emqx/license.md

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+View [license information](https://github.com/emqx/emqx/blob/master/LICENSE) for the software contained in this image.

emqx/maintainer.md

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+[EMQ Technologies](https://github.com/emqx)