AWS上具有Terraform的多个可用性区域 [英] Multiple availability zones with terraform on AWS

问题描述

我正在使用的VPC具有3个逻辑层：Web，App和DB。对于每个层，每个可用性区域中都有一个子网。我正在使用的区域中共有6个子网。

The VPC I'm working on has 3 logical tiers: Web, App and DB. For each tier there is one subnet in each availability zone. Total of 6 subnets in the region I'm using.

我正在尝试使用模块和 count 参数，但我不知道如何告诉terraform使用App层的两个子网。我的另一个限制是使用静态IP地址（或使用具有确定性的私有名称的方式）

I'm trying to create EC2 instances using a module and the count parameter but I don't know how to tell terraform to use the two subnets of the App tier. An additional constraint I have is to use static IP addresses (or a way to have a deterministic private name)

我在玩弄资源

resource "aws_instance" "app_server" {
  ...
  count = "${var.app_servers_count}"

  # Not all at the same time, though!
  availability_zone = ...
  subnet_id = ...
  private_ip = ...
}

到目前为止我已经尝试过/想到的事情：

Things I've tried/thought so far:

• 使用数据 aws_subnet all_app_subnets {...} ，按名称过滤，获取所有匹配的子网并将其用作列表。但是 aws_subnet 无法返回列表；


• 使用 data aws_availability_zones {...} 查找所有区域。但是我仍然有分配正确子网的问题；


• 使用 data aws_subnet_ids {...} 最好的选择。但是显然，它没有用于匹配网络名称的过滤器选项。


• 将子网ID作为字符串列表传递给模块。但是我不想硬编码ID，这不是自动化；


• 将子网硬编码为 data aws_subnet app_subnet_1 {...} ，数据 aws_subnet app_subnet_2 {...} ，但是我必须为每个子网使用不同的变量集， t like;


• 像上面提到的那样获取每个子网的信息，然后创建一个地图以列表的形式进行访问。但是不可能在变量定义中使用插值；


• 不使用模块并为每个环境对每个实例进行硬编码。嗯...真的吗？

• Use data "aws_subnet" "all_app_subnets" {...}, filter by name, get all the subnets that match and use them as a list. But aws_subnet cannot return a list;
• Use data "aws_availability_zones" {...} to find all the zones. But I still have the problem of assigning the correct subnet;
• Use data "aws_subnet_ids" {...} which looks like the best option. But apparently it doesn't have a filter option to match the networks namel
• Pass the subnets IDs as list of strings to the module. But I don't want to hard code the IDs, it's not automation;
• Hard code the subnets as data "aws_subnet" "app_subnet_1" {...}, data "aws_subnet" "app_subnet_2" {...} but then I have to use separate sets of variables for each subnet which I don't like;
• Get information for each subnet like in the point above but then create a map to access it as a list. But it's not possibile to use interpolation in variables definition;
• Not using modules and hard-code each instance for each environment. Mmmm... really?

我真的没有想法了。似乎没有人需要在特定子网中部署实例并保持良好的抽象度。我仅看到未指定子网或人们仅对所有内容使用默认值的示例。

I really ran out of ideas. It seems that nobody has to deploy instances in specific subnetworks and keep a good degree of abstration. I see only examples where subnetworks are not specified or where people just use default values for everything. Is this really something so unusual?

在此先感谢大家。

推荐答案

最后，我想出了解决方法，使用 data aws_subnet_ids {...} ，更重要的是理解terraform在使用时会从资源中创建列表 count ：

At the end I figured out how to do it, using data "aws_subnet_ids" {...} and more importantly understanding that terraform creates lists out of resources when using count:

variable "target_vpc" {}
variable "app_server_count" {}
variable "app_server_ip_start" {}

# Discover VPC
data "aws_vpc" "target_vpc" {
  filter = {
    name = "tag:Name"
    values = ["${var.target_vpc}"]
  }
}

# Discover subnet IDs. This requires the subnetworks to be tagged with Tier = "AppTier"
data "aws_subnet_ids" "app_tier_ids" {
  vpc_id = "${data.aws_vpc.target_vpc.id}"
  tags {
    Tier = "AppTier"
  }
}

# Discover subnets and create a list, one for each found ID
data "aws_subnet" "app_tier" {
  count = "${length(data.aws_subnet_ids.app_tier_ids.ids)}"
  id = "${data.aws_subnet_ids.app_tier_ids.ids[count.index]}"
}

resource "aws_instance" "app_server" {
  ...

  # Create N instances
  count = "${var.app_server_count}"

  # Use the "count.index" subnet
  subnet_id = "${data.aws_subnet_ids.app_tier_ids.ids[count.index]}"

  # Create an IP address using the CIDR of the subnet
  private_ip = "${cidrhost(element(data.aws_subnet.app_tier.*.cidr_block, count.index), var.app_server_ip_start + count.index)}"

  ...
}

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