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Add GitHub OIDC authentication for review app deployments
Add GitHub Actions OIDC identity provider in the integration account and create per-repository IAM roles for forms-admin, forms-runner, and forms-product-page. These roles allow GitHub-hosted runners to authenticate to AWS and deploy review apps. The IAM roles are scoped to pull_request events only and have permissions limited to the resources needed for review app deployments (ECS services, task definitions, ECR, S3 state files, and application autoscaling).
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‎infra/deployments/integration/account/github-auth.tf‎

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resource "aws_iam_openid_connect_provider" "github" {
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url = "https://token.actions.githubusercontent.com"
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client_id_list = ["sts.amazonaws.com"]
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thumbprint_list = ["7560d6f40fa55195f740ee2b1b7c0b4836cbe103"] # echo | openssl s_client -servername token.actions.githubusercontent.com -showcerts -connect token.actions.githubusercontent.com:443 2>/dev/null | openssl x509 -fingerprint -sha1 -noout | sed 's/://g' | awk -F= '{print tolower($2)}'
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}

‎infra/deployments/integration/account/outputs.tf‎

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@@ -16,3 +16,8 @@ output "codeconnection_arn" {
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output "kinesis_subscription_role_arn" {
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value = aws_iam_role.kinesis_subscription_role.arn
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}
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output "github_oidc_provider_arn" {
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description = "The ARN of the GitHub OIDC provider"
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value = aws_iam_openid_connect_provider.github.arn
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}

‎infra/deployments/integration/review/github_actions_oidc.tf‎

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locals {
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github_actions_apps = {
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"forms-admin" = {
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ecr_repository_arn = module.forms_admin_container_repo.arn
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}
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"forms-runner" = {
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ecr_repository_arn = module.forms_runner_container_repo.arn
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}
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"forms-product-page" = {
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ecr_repository_arn = module.forms_product_page_container_repo.arn
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}
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}
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}
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resource "aws_iam_role" "github_actions" {
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for_each = local.github_actions_apps
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name = "review-github-actions-${each.key}"
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description = "Role assumed by GitHub Actions workflows for ${each.key} review apps"
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assume_role_policy = jsonencode({
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Version = "2012-10-17"
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Statement = [
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{
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Effect = "Allow"
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Action = "sts:AssumeRoleWithWebIdentity"
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Principal = {
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Federated = data.terraform_remote_state.account.outputs.github_oidc_provider_arn
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}
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Condition = {
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StringEquals = {
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"token.actions.githubusercontent.com:aud" = "sts.amazonaws.com"
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}
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StringLike = {
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"token.actions.githubusercontent.com:sub" = "repo:alphagov/${each.key}:pull_request"
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}
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}
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}
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]
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})
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}
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resource "aws_iam_role_policy" "github_actions" {
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for_each = local.github_actions_apps
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role = aws_iam_role.github_actions[each.key].name
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policy = data.aws_iam_policy_document.github_actions[each.key].json
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}
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data "aws_iam_policy_document" "github_actions" {
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for_each = local.github_actions_apps
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statement {
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sid = "UseECSServices"
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effect = "Allow"
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actions = [
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"ecs:*Service",
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"ecs:*Services",
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"ecs:TagResource"
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]
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resources = [
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aws_ecs_cluster.review.arn,
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"arn:aws:ecs:eu-west-2:${data.aws_caller_identity.current.account_id}:service/${aws_ecs_cluster.review.name}/${each.key}-pr-*"
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]
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}
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statement {
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sid = "UseECSTaskDefinitions"
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effect = "Allow"
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actions = [
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"ecs:*TaskDefinition",
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"ecs:*TaskDefinitions",
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"ecs:TagResource"
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]
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resources = [
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"arn:aws:ecs:eu-west-2:${data.aws_caller_identity.current.account_id}:task-definition/${each.key}-pr-*"
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]
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}
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statement {
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sid = "AllowTaskDefinitionsNeedingStar"
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effect = "Allow"
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actions = [
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"ecs:DeregisterTaskDefinition",
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"ecs:DescribeTaskDefinition"
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]
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resources = ["*"]
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}
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statement {
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sid = "ReadTerraformStateFiles"
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effect = "Allow"
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actions = [
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"s3:GetObject",
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"s3:GetObjectVersion",
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"s3:HeadObject",
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"s3:ListBucket"
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]
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resources = [
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"arn:aws:s3:::gds-forms-integration-tfstate",
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"arn:aws:s3:::gds-forms-integration-tfstate/review.tfstate",
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"arn:aws:s3:::gds-forms-integration-tfstate/review-apps/${each.key}/pr-*.tfstate"
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]
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}
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statement {
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sid = "WriteTerraformStateFiles"
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effect = "Allow"
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actions = [
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"s3:PutObject",
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"s3:PutObjectVersion"
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]
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resources = [
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"arn:aws:s3:::gds-forms-integration-tfstate/review-apps/${each.key}/pr-*.tfstate"
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]
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}
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statement {
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sid = "ReleaseTerraformStateLock"
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actions = [
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"s3:DeleteObject",
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]
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resources = [
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"arn:aws:s3:::gds-forms-integration-tfstate/review-apps/${each.key}/pr-*.tflock"
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]
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effect = "Allow"
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}
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statement {
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sid = "UseLocalECR"
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effect = "Allow"
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actions = [
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"ecr:BatchCheckLayerAvailability",
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"ecr:BatchGetImage",
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"ecr:CompleteLayerUpload",
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"ecr:GetDownloadUrlForLayer",
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"ecr:InitiateLayerUpload",
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"ecr:PutImage",
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"ecr:UploadLayerPart",
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]
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resources = [
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each.value.ecr_repository_arn
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]
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}
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statement {
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sid = "LogIntoLocalECR"
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effect = "Allow"
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actions = [
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"ecr:GetAuthorizationToken",
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]
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resources = [
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"*"
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]
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}
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statement {
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sid = "UseDeployECR"
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effect = "Allow"
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actions = [
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"ecr:BatchCheckLayerAvailability",
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"ecr:BatchGetImage",
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"ecr:GetDownloadUrlForLayer"
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]
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resources = [
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"arn:aws:ecr:eu-west-2:${var.deploy_account_id}:repository/*"
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]
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}
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statement {
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sid = "AllowIAMPassRole"
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effect = "Allow"
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actions = [
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"iam:PassRole"
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]
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resources = [
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aws_iam_role.ecs_execution.arn,
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aws_iam_service_linked_role.app_autoscaling.arn,
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]
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}
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statement {
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sid = "UseAppAutoscaling"
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effect = "Allow"
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actions = [
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"application-autoscaling:*ScalableTarget",
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"application-autoscaling:*ScalableTargets",
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"application-autoscaling:*ScheduledAction",
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"application-autoscaling:*ScheduledActions",
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"application-autoscaling:*ScalingPolicy",
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"application-autoscaling:*ScalingPolicies",
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"application-autoscaling:ListTagsForResource",
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"application-autoscaling:TagResource",
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"application-autoscaling:UntagResource"
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]
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resources = [
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"arn:aws:application-autoscaling:eu-west-2:${data.aws_caller_identity.current.account_id}:scalable-target/*"
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]
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}
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statement {
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sid = "UseAppAutoscalingNeedingStar"
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effect = "Allow"
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actions = [
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"application-autoscaling:DescribeScalableTargets",
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"application-autoscaling:DescribeScalingPolicies",
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"application-autoscaling:DescribeScheduledActions",
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]
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resources = [
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"*"
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]
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}
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}

‎infra/deployments/integration/review/outputs.tf‎

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@@ -48,3 +48,10 @@ output "traefik_basic_auth_credentials" {
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value = data.aws_ssm_parameter.traefik_basic_auth_credentials.value
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sensitive = true
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}
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output "github_actions_role_arns" {
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description = "IAM role ARNs for GitHub Actions review app deployments"
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value = {
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for app, role in aws_iam_role.github_actions : app => role.arn
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}
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}

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