aboutsummaryrefslogtreecommitdiff
path: root/content/blog/aws/defaults.md
blob: 454b32565fc99113dd03c2c26b521f5d0738c2ba (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
---
title: Securing AWS default VPCs
description: With terraform/OpenTofu
date: 2024-09-10
tags:
- aws
- OpenTofu
- terraform
---

## Introduction

AWS offers some network conveniences in the form of a default VPC, default security group (allowing access to the internet) and default routing table. These exist in all AWS regions your accounts have access to, even if never plan to deploy anything there. And yes most AWS regions cannot be disabled entirely, only the most recent ones can be.

I feel the need to clean up these resources in order to prevent any misuse. Most people do not understand networking and some could inadvertently spawn instances with public IP addresses. By making the default VPC inoperative, these people need to come to someone more knowledgeable before they do anything foolish.

## Module

The special default variants of the following AWS terraform resources are quirky: defining them does not create anything but automatically import the built-in aws resources and then edit their attributes to match your configuration. Furthermore, destroying these resources would only remove them from your state.

``` hcl
resource "aws_default_vpc" "default" {
  tags = { Name = "default" }
}

resource "aws_default_security_group" "default" {
  ingress = []
  egress  = []
  tags    = { Name = "default" }
  vpc_id  = aws_default_vpc.default.id
}

resource "aws_default_route_table" "default" {
  default_route_table_id = aws_default_vpc.default.default_route_table_id
  route                  = []
  tags                   = { Name = "default - empty" }
}
```

The key here (and initial motivation for this article) is the `ingress = []` expression syntax (or `egress` or `route`): while these attributes are normally block attributes, you can also use them in a `= []` expression in order to express that you want to enforce the resource not having any ingress, egress or route rules. Defining the resources without any block rules would just leave these attributes untouched.

## Iterating through all the default regions

As I said, most AWS regions cannot be disabled entirely, only the most recent ones can be. It is currently not possible to instanciate terraform providers on the fly, but thankfully it is coming in a future OpenTofu release! In the meantime, we need to do these kinds of horrors:

``` hcl
provider "aws" {
  alias   = "ap-northeast-1"
  profile = var.environment
  region  = "ap-northeast-1"
  default_tags { tags = { "managed-by" = "tofu" } }
}

provider "aws" {
  alias   = "ap-northeast-2"
  profile = var.environment
  region  = "ap-northeast-2"
  default_tags { tags = { "managed-by" = "tofu" } }
}

provider "aws" {
  alias   = "ap-northeast-3"
  profile = var.environment
  region  = "ap-northeast-3"
  default_tags { tags = { "managed-by" = "tofu" } }
}

provider "aws" {
  alias   = "ap-south-1"
  profile = var.environment
  region  = "ap-south-1"
  default_tags { tags = { "managed-by" = "tofu" } }
}

provider "aws" {
  alias   = "ap-southeast-1"
  profile = var.environment
  region  = "ap-southeast-1"
  default_tags { tags = { "managed-by" = "tofu" } }
}

provider "aws" {
  alias   = "ap-southeast-2"
  profile = var.environment
  region  = "ap-southeast-2"
  default_tags { tags = { "managed-by" = "tofu" } }
}

provider "aws" {
  alias   = "ca-central-1"
  profile = var.environment
  region  = "ca-central-1"
  default_tags { tags = { "managed-by" = "tofu" } }
}

provider "aws" {
  alias   = "eu-central-1"
  profile = var.environment
  region  = "eu-central-1"
  default_tags { tags = { "managed-by" = "tofu" } }
}

provider "aws" {
  alias   = "eu-north-1"
  profile = var.environment
  region  = "eu-north-1"
  default_tags { tags = { "managed-by" = "tofu" } }
}

provider "aws" {
  alias   = "eu-west-1"
  profile = var.environment
  region  = "eu-west-1"
  default_tags { tags = { "managed-by" = "tofu" } }
}

provider "aws" {
  alias   = "eu-west-2"
  profile = var.environment
  region  = "eu-west-2"
  default_tags { tags = { "managed-by" = "tofu" } }
}

provider "aws" {
  alias   = "eu-west-3"
  profile = var.environment
  region  = "eu-west-3"
  default_tags { tags = { "managed-by" = "tofu" } }
}

provider "aws" {
  alias   = "sa-east-1"
  profile = var.environment
  region  = "sa-east-1"
  default_tags { tags = { "managed-by" = "tofu" } }
}

provider "aws" {
  alias   = "us-east-1"
  profile = var.environment
  region  = "us-east-1"
  default_tags { tags = { "managed-by" = "tofu" } }
}

provider "aws" {
  alias   = "us-east-2"
  profile = var.environment
  region  = "us-east-2"
  default_tags { tags = { "managed-by" = "tofu" } }
}

provider "aws" {
  alias   = "us-west-1"
  profile = var.environment
  region  = "us-west-1"
  default_tags { tags = { "managed-by" = "tofu" } }
}

provider "aws" {
  alias   = "us-west-2"
  profile = var.environment
  region  = "us-west-2"
  default_tags { tags = { "managed-by" = "tofu" } }
}

module "ap-northeast-1" {
  providers = { aws = aws.ap-northeast-1 }
  source    = "../modules/defaults"
}

module "ap-northeast-2" {
  providers = { aws = aws.ap-northeast-2 }
  source    = "../modules/defaults"
}

module "ap-northeast-3" {
  providers = { aws = aws.ap-northeast-3 }
  source    = "../modules/defaults"
}

module "ap-south-1" {
  providers = { aws = aws.ap-south-1 }
  source    = "../modules/defaults"
}

module "ap-southeast-1" {
  providers = { aws = aws.ap-southeast-1 }
  source    = "../modules/defaults"
}

module "ap-southeast-2" {
  providers = { aws = aws.ap-southeast-2 }
  source    = "../modules/defaults"
}

module "ca-central-1" {
  providers = { aws = aws.ca-central-1 }
  source    = "../modules/defaults"
}

module "eu-central-1" {
  providers = { aws = aws.eu-central-1 }
  source    = "../modules/defaults"
}

module "eu-north-1" {
  providers = { aws = aws.eu-north-1 }
  source    = "../modules/defaults"
}

module "eu-west-1" {
  providers = { aws = aws.eu-west-1 }
  source    = "../modules/defaults"
}

module "eu-west-2" {
  providers = { aws = aws.eu-west-2 }
  source    = "../modules/defaults"
}

module "eu-west-3" {
  providers = { aws = aws.eu-west-3 }
  source    = "../modules/defaults"
}

module "sa-east-1" {
  providers = { aws = aws.sa-east-1 }
  source    = "../modules/defaults"
}

module "us-east-1" {
  providers = { aws = aws.us-east-1 }
  source    = "../modules/defaults"
}

module "us-east-2" {
  providers = { aws = aws.us-east-2 }
  source    = "../modules/defaults"
}

module "us-west-1" {
  providers = { aws = aws.us-west-1 }
  source    = "../modules/defaults"
}

module "us-west-2" {
  providers = { aws = aws.us-west-2 }
  source    = "../modules/defaults"
}
```

## Conclusion

Terraform is absolutely quirky at times, but it is not its fault here: the AWS provider and their magical default resources are.