微服务实践——Docker与服务发现

Posted 2021-04-21 架构师

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Docker Java App Load Balanced By nginx Or Apache HTTP, Mongo Replica Set And Hazelcast Cluster

背景

为了发挥Docker在跨多个服务器的分布式应用程序的部署（甚至是跨区域）的能力，人们不应该限制哪些服务进到哪个服务器。动态可扩展性（或自动缩放）的关键环境的要求（如生产环境）不只是适用于新的微服务架构设计。也适用于典型的单片应用程序的部署。如果这些服务绑定在特定的服务器上，那么这些程序的未来的可扩展性是很困难的。

为了能够实现服务发现，我们需要满足以下条件：

Service registration 在服务器上保存这些正在运行服务的端口。
Service discovery 实现发现我们在服务器保存在注册过程中的信息

我们还要实现强的服务，以满足企业级对服务发现的要求。包括以下这些问题：

我们如何注销停止工作的服务?
我们如何对这些”发现了的”服务实施负载均衡?
如果服务在横向扩展或者缩放的过程中被删除了怎么办?

大多数典型的服务发现工具拥有某种高度可用的分布式（key/value）存储，大家可以参考阅读这篇博客http://technologyconversations.com/2015/09/08/service-discovery-zookeeper-vs-etcd-vs-consul/

这些工具的主要缺点是他们自己在容器中运行对第三方工具的依赖。为了使用Consul，打个比方。一个用户需要在程序中使用Consul 和Registrator 容器-这一定会使容器的数量增加。那么用户就需要管理这些容器。

DCHQ，从另一方面说。如果使用代理来协调服务注册和服务发现。把信息存储在底层DCHQ数据库。这意味着我们不需要附加的容器。另外，服务发现框架，允许用户自定义某些事件需要被执行的同时，利用的不只是IP和应用程序中的其他容器的主机名的信息提供了更大的灵活性。在部署的时候使用的也是环境变量的值。

这并不等于说服务发现框架使用DHCQ就能完全替代其它工具，最好的工具还是能够满足业务的需求。

在这篇blog中，我们将介绍使用Docker部署3个服务发现的程序，包括：Nginx & Apache HTTP Server load balancing, Mongo Replica Set and Hazelcast Cluster.

包括以下内容：

构建能够在任意Linux 主机上面运行的YAML-based 程序模板
在任何云基础架构上的配置和自动扩展（本文我们以Microsoft Azure为例）
在Microsoft Azure集群部署分布式，高可用性应用程序
监控运行容器的 CPU, Memory & I/O
Tomacat 应用服务集群扩展
MongoDB的分片服务扩展
Hazelcast 集群扩展

构建能够在任意Linux 主机上面运行的YAML-based 程序模板

用户一旦登录到DCHQ (either the hosted DCHQ.io or on-premise version)，用户可以导航到Manage>App/Machine，然后可以点击+创建新的Docker Compose模板

我们使用 Docker Hub官方镜像创建了5 个程序的模板

这些模板包括了一下程序栈：

Multi-Tier Java Application with Nginx, Tomcat, Solr and Mongo — using Consul and Registrator for service discovery
Multi-Tier Java Application with Nginx, Tomcat, Solr and Mongo — using DCHQ’s service discovery framework
Multi-Tier Java Application with Apache HTTP Server, Tomcat, Solr, and Cassandra) — using DCHQ’s service discovery framework
Mongo Replica Set — using DCHQ’s service discovery framework
Hazelcast Cluster — using DCHQ’s service discovery framework

更多关于Docker application modeling in DCHQ的资料可以访问： http://dchq.co/docker-compose.html

更多关于Docker service discovery in DCHQ的资料可以访问： http://dchq.co/docker-service-discovery.html

Request Time & Post-Provision 的Web Servers 和 Application Servers配置插件

通过这些程序的模板，你会发现一些容器为了配置容器会调用Bash脚本插件。这些脚本对post-provision操作执行的非常好。

这些插件可以在Manage > Plug-ins导航中创建，一旦这些脚本启动是，DHCQ代理服务会执行这些容器里面的脚本。用户可以指定一个能被在请求之后被覆盖的参数。在$符号之前的都可以被成为参数，比如：$file_url 可以是一个参数，它允许开发者指定的网址下载一个WAR文件，还可以在当用户希望更新运行在容器上例如Java WAR文件请求时间和后规定被覆盖：

该插件ID需要在定义YAML应用程序模板时候提供，例如：调用Nginxbash脚本插件。我们可以参照下面的plug-in ID：

你会发现，同样的Nginx插件，在不同的阶段得到了执行。

当 Nginx 容器创建的时候 — 在这种情况下, 应用程序的容器IP会被注入到默认配置文件下面。以便实现服务的负载均衡。

然而这里的服务发现框架同时做着服务发现和服务注册的事情。

服务发现插件的生命周期

on_create — executes the plug-in when creating the container
on_start — executes the plug-in after a container starts
on_stop — executes the plug-in before a container stops
on_destroy — executes the plug-in before destroying a container
post_create — executes the plug-in after the container is created and running
post_start[:Node] — executes the plug-in after another container starts
post_stop[:Node] — executes the plug-in after another container stops
post_destroy[:Node] — executes the plug-in after another container is destroyed
post_scale_out[:Node] — executes the plug-in after another cluster of containers is scaled out
post_scale_in[:Node] — executes the plug-in after another cluster of containers is scaled in

要访问Nginx, Apache HTTP Server (httpd), Mongo Replica Set, and Hazelcast Cluster需要遵循EULA许可。

Sign Up for FREE on DCHQ.io — http://dchq.io (no credit card required)
Download DCHQ On-Premise Standard Edition for FREE — http://dchq.co/dchq-on-premise-download.html

配置部署在多台主机HA的 cluster_size 与host 参数

host1, host2, host3, etc. – selects a host randomly within a data-center (or cluster) for container deployments
IP Address 1, IP Address 2, etc. — allows a user to specify the actual IP addresses to use for container deployments
Hostname 1, Hostname 2, etc. — allows a user to specify the actual hostnames to use for container deployments
Wildcards (e.g. “db-”, or “app-srv-”) – to specify the wildcards to use within a hostname

通过镜像绑定环境变量

{{alphanumeric | 8}} – creates a random 8-character alphanumeric string. This is most useful for creating random passwords.
{{Image Name | ip}} – allows you to enter the host IP address of a container as a value for an environment variable. This is most useful for allowing the middleware tier to establish a connection with the database.
{{Image Name | container_ip}} – allows you to enter the name of a container as a value for an environment variable. This is most useful for allowing the middleware tier to establish a secure connection with the database (without exposing the database port).
{{Image Name | container_private_ip}} – allows you to enter the internal IP of a container as a value for an environment variable. This is most useful for allowing the middleware tier to establish a secure connection with the database (without exposing the database port).
{{Image Name | port_Port Number}} – allows you to enter the Port number of a container as a value for an environment variable. This is most useful for allowing the middleware tier to establish a connection with the database. In this case, the port number specified needs to be the internal port number – i.e. not the external port that is allocated to the container. For example, {{PostgreSQL | port_5432}} will be translated to the actual external port that will allow the middleware tier to establish a connection with the database.
{{Image Name | Environment Variable Name}} – allows you to enter the value an image’s environment variable into another image’s environment variable. The use cases here are endless – as most multi-tier applications will have cross-image dependencies.

构建 Nginx Docker 镜像的 Consul

Git URL – https://github.com/dchqinc/nginx-consul.git
Git Branch – this field is optional — but a user can specify a branch from a GitHub project. The default branch is master.
Git Credentials – a user can store the credentials to a private GitHub repository securely in DCHQ. This can be done by navigating toManage > Cloud Providers and Repos and clicking on the + to select Credentials
Cluster – the building of Docker images is orchestrated through the DCHQ agent. As a result, a user needs to select a cluster on which an agent will be used to execute the building of Docker images. If a cluster has not been created yet, please refer to this sectionto either register already running hosts or automate the provisioning of new virtual infrastructure.
Push to Registry – a user can push the newly created image on either a public or private repository on Docker Hub or Quay. To register a Docker Hub or Quay account, a user should navigate toManage > Cloud Providers and clicking on the + to select Docker Registries
Repository – this is the name of the repository on which the image will be pushed. For example, our image was pushed todchq/nginx-consul:latest
Tag – this is the tag name that you would like to give for the new image. The supported tag names in DCHQ include:

{{date}} — formatted date
{{timestamp}} — the full time-stamp

Cron Expression – a user can schedule the building of Docker images using out-of-box cron expressions. This facilitates daily and nightly builds for users.

Multi-Tier Java (Consul-Nginx-Tomcat-Solr-Mongo)

Nginx:
  image: dchqinx-consul:latest
  publish_all: true
  mem_min: 50m
  host: host1
  plugins:
    - !plugin
      id: GINmu
      restart: true
      lifecycle: on_create
      arguments:
        - APPSERVER_IP={{AppServer | container_private_ip}}
        - SERVICE_NAME={{AppServer | SERVICE_NAME}}
        - SERVICE_TAGS={{AppServer | SERVICE_TAGS}}
        - CONSUL_IP={{Consul | container_private_ip}}

AppServer:
  image: tomcat:8.0.21-jre8
  mem_min: 600m
  host: host1
  cluster_size: 1
  environment:
    - mongo_url={{Mongo|container_private_ip}}:27017/dchq
    - solr_host={{Solr|container_private_ip}}
    - solr_port=8983
    - SERVICE_NAME=app
    - SERVICE_TAGS=production
  plugins:
    - !plugin
      id: oncXN
      restart: true
      arguments:
        - file_url=https://github.com/dchqinc/dchq-docker-java-solr-mongo-cassandra-example/raw/master/dbconnect.war
        - dir=/usr/local/tomcat/webapps/ROOT.war
        - delete_dir=/usr/local/tomcat/webapps/ROOT
Consul:
  image: progrium/consul:latest
  host: host1
  ports:
    - "8300:8300"
    - "8400:8400"
    - "8500:8500"
    - "8600:53/udp"
  command: -server -bootstrap -advertise 10.0.2.15

Registrator:
  image: gliderlabs/registrator:latest
  host: host1
  command: consul://<HOST_IP>:8500
  volumes:
    - "ar/run/docker.sock:/tmp/docker.sock"

Solr:
  image: solr:latest
  mem_min: 300m
  host: host1
  publish_all: false
  plugins:
    - !plugin
      id: doX8s
      restart: true
      arguments:
        - file_url=https://github.com/dchqinc/dchq-docker-java-solr-mongo-cassandra-example/raw/master/names.zip
Mongo:
  image: mongo:latest
  host: host1
  mem_min: 400m

来源：谢权'blog

原文：https://xiequan.info/在docker上运行微服务实践/

转载文章，向原作者致敬！如有侵权或不周之处，敬请劳烦联系若飞（微信：1321113940）马上删除，谢谢！

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