AWS 上具有 terraform 的多个可用区 [英] Multiple availability zones with terraform on AWS

问题描述

我正在处理的 VPC 有 3 个逻辑层:Web、应用程序和数据库.对于每一层，每个可用区中有一个子网.我使用的区域中共有 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 参数创建 EC2 实例，但我不知道如何告诉 terraform 使用应用层的两个子网.我的另一个限制是使用静态 IP 地址(或具有确定性私有名称的方法)

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 = ...
}

到目前为止我尝试/想到的事情:

Things I've tried/thought so far:

• 使用data "aws_subnet" "all_app_subnets" {...}，按名称过滤，获取所有匹配的子网并将它们用作列表.但是 aws_subnet 不能返回列表；
• 使用 data "aws_availability_zones" {...} 查找所有区域.但是我仍然存在分配正确子网的问题；
• 使用 data "aws_subnet_ids" {...} 这看起来是最好的选择.但显然它没有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.但我不想对 ID 进行硬编码，这不是自动化；
• 将子网硬编码为 data "aws_subnet" "app_subnet_1" {...}, data "aws_subnet" "app_subnet_2" {...} 但后来我必须为我不喜欢的每个子网使用单独的变量集；
• 像上面那样获取每个子网的信息，然后创建一个 map 以将其作为列表访问.但是不能在变量定义中使用插值；
• 不使用模块并对每个环境的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.似乎没有人必须在特定的子网中部署实例并保持良好的抽象程度.我只看到未指定子网或人们只对所有内容使用默认值的示例.这真的有那么不寻常吗?

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?

先谢谢大家.

推荐答案

最后我想出了怎么做，使用 data "aws_subnet_ids" {...} 更重要的是理解terraform 在使用 count 时创建资源列表:

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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