RabbitMQ 3.5.7 发布 AMQP 消息服务器

RabbitMQ 3.5.7 是一个可用的 bug 修复版本，主要更新如下：

服务器

Bug 修复

Fix a race condition that could prevent nodes from stopping.
GitHub issue:rabbitmq-server#465
file_handle_cache:clear_read_cache/0 no longer silently fails.
The function is mean to be used with rabbitmqctl eval in environments where
in-process buffering of file data is enabled.

GitHub issue: rabbitmq-server#436
Default RABBITMQ_PLUGINS_DIR value on Windows should be calculated as relative to RabbitMQ
server installation directory, not RABBITMQ_BASE.

If you override RABBITMQ_BASE, you may need to copy plugins from %RABBITMQ_BASE%\plugins
to the plugins directory under RabbitMQ installation.

GitHub issue: rabbitmq-server#433
When rabbitmq-server failed to start due to an unreadable config file, exit code was 0
GitHub issue: rabbitmq-server#464
Overriding RABBITMQ_LOGS and RABBITMQ_SASL_LOGS on Windows prevented node from starting.
GitHub issue: rabbitmq-server#375
Some startup code bits assumed IPv4 is enabled in the environment
GitHub issue: rabbitmq-server#117
More robust disk monitor, fewer errors logged.
GitHub issue: rabbitmq-server#91
rabbitmqctl forget_cluster_node no longer attempts to impersonate live
(reachable) nodes.

GitHub issue: rabbitmq-server#470
rabbitmq-plugins was using an incorrect env variable.
GitHub issue: rabbitmq-server#451

提升

RAM watermark can be configured as an absolute value in bytes (just like with disk space monitoring):
```
[{rabbit, [{vm_memory_high_watermark, {absolute, 1073741824}}]}].
```
GitHub issue: rabbitmq-server#207
rabbitmqctl authenticate_user is a new command that can be used to test user authentication.
GitHub issue: rabbitmq-server#119
rabbitmqctl now supports exclusive as a queue info item.
Contributed by Alexey Lebedeff (@binarin).

GitHub issue: rabbitmq-server#371

RabbitMQ 是由 LShift 提供的一个 Advanced Message Queuing Protocol (AMQP) 的开源实现，由以高性能、健壮以及可伸缩性出名的 Erlang 写成，因此也是继承了这些优点。

AMQP 里主要要说两个组件：Exchange 和 Queue （在 AMQP 1.0 里还会有变动），如下图所示，绿色的 X 就是 Exchange ，红色的是 Queue ，这两者都在 Server 端，又称作 Broker ，这部分是 RabbitMQ 实现的，而蓝色的则是客户端，通常有 Producer 和 Consumer 两种类型：