【Terraform】快速实践"Hello World"

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专栏上文已经简单介绍了Terraform以及其安装，这篇文章根据社区教程，编写一个基于Docker启动nginx的例子。

一、环境准备

Terraform 和 Docker

在正式开始例子之前，我们必须保证环境中已经安装了Terraform、docker，前者参照专栏内部的上篇文章，docker的安装参照这篇文章《文章TODO》。

Provider插件缓存配置

在Terraform的整个执行流程中，我们在使用到Terraform init命令时，该工具会分析我们代码中使用到的Provider，并尝试下载Provider插件到本地，如果我们不进行特殊的设置，每次执行init都会尝试去下载插件，并且每个项目都回保存自己独立的插件，相当浪费空间。这怎么办呢？

这时我们可以使用插件缓存,基本的原理只要插件下载成功一次，就会保存在指定的插件缓存目录，其它项目再次下载，就会拷贝缓存内容到项目目录，甚至在系统支持上，Terraform还会使用符号连接这个缓存路径，并不直接拷贝插件内容。

有两种方式，第一种方式是配置TF_PLUGIN_CACHE_DIR环境变量：

#务必确保这个目录下已经创建好plugin-cache这个文件夹
export TF_PLUGIN_CACHE_DIR="$HOME/.terraform.d/plugin-cache"
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第二种方式是使用CLI配置文件，基于Linux环境，在用户的/home目录下创建名为 ".terraformrc" 的文件：

plugin_cache_dir = "$HOME/.terraform.d/plugin-cache"
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需要注意的是：有必要关注缓存路径的空间增长，择机选择性地手工清理不必要的Provider插件。

二、实战

这次实战的目的是通过Terraform部署基于Docker的Nginx环境，并能成功访问到Nginx的欢迎主页。

2.1 定义资源

在这里我们使用到Github上的项目

[terraform-provider-docker​]  github.com/kreuzwerker…

提供的Provider插件，编写资源文件main.tf。

terraform {
#定义所需的Provider
  required_providers {
    docker = {
      source  = "kreuzwerker/docker"
      version = "~> 2.13.0"
    }
  }
}
​
# 配置docker provider
provider "docker" {}
​
#创建一个docker镜像资源
 resource "docker_image" "nginx" {
  name         = "nginx:latest"
  keep_locally = false
}
#创建一个docker容器资源
#这部分的资源定义，类似"docker run --name nginx -p8080:80 -d nginx:latest"
resource "docker_container" "nginx" {
  image = docker_image.nginx.latest
  name  = "tutorial"
  ports {
    internal = 80
    external = 8000
  }
}
#接下来还可以继续定义服务资源
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2.2 执行创建

关于基础设施的资源已经定义完成，接下来就是在安装好Terraform和docker的服务器上执行部署。

首先，为了区分项目，达到隔离资源的目的，我们先在工程目录创建一个新文件夹：

#创建目录
$mkdir learn-terraform-docker-container
#进入目录
$cd learn-terraform-docker-container
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然后上传main.tf到当前文件夹。接着在当前目录执行Terraform init初始化环境。

$Terraform init
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小提示：环境初始过程花费的时间会与你的服务器网络环境密切相关，请耐心等待，如果失败，请多尝试几次！

如图上所示，环境初始化成功，观察本地目录，多了一些文件和文件夹。

.terraform隐藏文件夹中存储着我们下载的Provider插件内容，.terraform.lock.hcl记录了provider插件的一些依赖信息。如果进入我们前面设置的缓存插件目录，会多了这个插件的内容。

接下来，我们预览资源部署情况terraform plan。

$terraform plan
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执行结果输出如下：

Terraform used the selected providers to generate the following execution plan. Resource actions are indicated with the following symbols:
  + create
​
Terraform will perform the following actions:
​
  # docker_container.nginx will be created
  + resource "docker_container" "nginx" {
      + attach           = false
      + bridge           = (known after apply)
      + command          = (known after apply)
      + container_logs   = (known after apply)
      + entrypoint       = (known after apply)
      + env              = (known after apply)
      + exit_code        = (known after apply)
      + gateway          = (known after apply)
      + hostname         = (known after apply)
      + id               = (known after apply)
      + image            = (known after apply)
      + init             = (known after apply)
      + ip_address       = (known after apply)
      + ip_prefix_length = (known after apply)
      + ipc_mode         = (known after apply)
      + log_driver       = "json-file"
      + logs             = false
      + must_run         = true
      + name             = "tutorial"
      + network_data     = (known after apply)
      + read_only        = false
      + remove_volumes   = true
      + restart          = "no"
      + rm               = false
      + security_opts    = (known after apply)
      + shm_size         = (known after apply)
      + start            = true
      + stdin_open       = false
      + tty              = false
​
      + healthcheck {
          + interval     = (known after apply)
          + retries      = (known after apply)
          + start_period = (known after apply)
          + test         = (known after apply)
          + timeout      = (known after apply)
        }
​
      + labels {
          + label = (known after apply)
          + value = (known after apply)
        }
​
      + ports {
          + external = 8000
          + internal = 80
          + ip       = "0.0.0.0"
          + protocol = "tcp"
        }
    }
​
  # docker_image.nginx will be created
  + resource "docker_image" "nginx" {
      + id           = (known after apply)
      + keep_locally = false
      + latest       = (known after apply)
      + name         = "nginx:latest"
      + output       = (known after apply)
      + repo_digest  = (known after apply)
    }
​
Plan: 2 to add, 0 to change, 0 to destroy.
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根据输出内容可以看到增加了两个资源，包括镜像和容器。无更改和销毁项。

接下来执行部署资源terraform apply。

$terraform apply
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执行结果输出如下：

Terraform used the selected providers to generate the following execution plan. Resource actions are indicated with the following symbols:
  + create
​
Terraform will perform the following actions:
​
  # docker_container.nginx will be created
  + resource "docker_container" "nginx" {
      + attach           = false
      + bridge           = (known after apply)
      + command          = (known after apply)
      + container_logs   = (known after apply)
      + entrypoint       = (known after apply)
      + env              = (known after apply)
      + exit_code        = (known after apply)
      + gateway          = (known after apply)
      + hostname         = (known after apply)
      + id               = (known after apply)
      + image            = (known after apply)
      + init             = (known after apply)
      + ip_address       = (known after apply)
      + ip_prefix_length = (known after apply)
      + ipc_mode         = (known after apply)
      + log_driver       = "json-file"
      + logs             = false
      + must_run         = true
      + name             = "tutorial"
      + network_data     = (known after apply)
      + read_only        = false
      + remove_volumes   = true
      + restart          = "no"
      + rm               = false
      + security_opts    = (known after apply)
      + shm_size         = (known after apply)
      + start            = true
      + stdin_open       = false
      + tty              = false
​
      + healthcheck {
          + interval     = (known after apply)
          + retries      = (known after apply)
          + start_period = (known after apply)
          + test         = (known after apply)
          + timeout      = (known after apply)
        }
​
      + labels {
          + label = (known after apply)
          + value = (known after apply)
        }
​
      + ports {
          + external = 8000
          + internal = 80
          + ip       = "0.0.0.0"
          + protocol = "tcp"
        }
    }
​
  # docker_image.nginx will be created
  + resource "docker_image" "nginx" {
      + id           = (known after apply)
      + keep_locally = false
      + latest       = (known after apply)
      + name         = "nginx:latest"
      + output       = (known after apply)
      + repo_digest  = (known after apply)
    }
​
Plan: 2 to add, 0 to change, 0 to destroy.
​
Do you want to perform these actions?
  Terraform will perform the actions described above.
  Only 'yes' will be accepted to approve.
​
  Enter a value:yes
​
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输入yes明确要执行部署。

部署完成！未出现错误。

然后查看docker容器中是否已经创建了nginx。

$docker ps
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有了，创建成功了，然后curl访问一下，也能获取到欢迎主页！

至此，部署创建成功，我们观察项目目录，多了一个terraform.tfstate文件，这个就是状态文件，相当重要，切记不要尝试去手动修改它！

2.3 执行销毁

执行销毁那是相当简单了，用项目目录下执行terraform destroy命令即可。

$terraform destroy
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