feat: Add use_cache_from_previous_image variable

examples/container-image/main.tf

@@ -128,7 +128,8 @@ module "docker_build_from_ecr" {
     dir_sha = local.dir_sha
   }
 
-  cache_from = ["${module.ecr.repository_url}:latest"]
+  cache_from                    = ["${module.ecr.repository_url}:latest"]
+  use_cache_from_previous_image = true
 }
 
 module "ecr" {

modules/docker-build/README.md

@@ -60,6 +60,7 @@ module "docker_image" {
 | <a name="requirement_terraform"></a> [terraform](#requirement\_terraform) | >= 1.0 |
 | <a name="requirement_aws"></a> [aws](#requirement\_aws) | >= 4.22 |
 | <a name="requirement_docker"></a> [docker](#requirement\_docker) | >= 3.0 |
+| <a name="requirement_external"></a> [external](#requirement\_external) | >= 2.3 |
 | <a name="requirement_null"></a> [null](#requirement\_null) | >= 2.0 |
 
 ## Providers
@@ -68,6 +69,7 @@ module "docker_image" {
 |------|---------|
 | <a name="provider_aws"></a> [aws](#provider\_aws) | >= 4.22 |
 | <a name="provider_docker"></a> [docker](#provider\_docker) | >= 3.0 |
+| <a name="provider_external"></a> [external](#provider\_external) | >= 2.3 |
 | <a name="provider_null"></a> [null](#provider\_null) | >= 2.0 |
 
 ## Modules
@@ -85,6 +87,7 @@ No modules.
 | [null_resource.sam_metadata_docker_registry_image](https://registry.terraform.io/providers/hashicorp/null/latest/docs/resources/resource) | resource |
 | [aws_caller_identity.this](https://registry.terraform.io/providers/hashicorp/aws/latest/docs/data-sources/caller_identity) | data source |
 | [aws_region.current](https://registry.terraform.io/providers/hashicorp/aws/latest/docs/data-sources/region) | data source |
+| [external_external.latest_ecr_image](https://registry.terraform.io/providers/hashicorp/external/latest/docs/data-sources/external) | data source |
 
 ## Inputs
 
@@ -109,6 +112,7 @@ No modules.
 | <a name="input_scan_on_push"></a> [scan\_on\_push](#input\_scan\_on\_push) | Indicates whether images are scanned after being pushed to the repository | `bool` | `false` | no |
 | <a name="input_source_path"></a> [source\_path](#input\_source\_path) | Path to folder containing application code | `string` | `null` | no |
 | <a name="input_triggers"></a> [triggers](#input\_triggers) | A map of arbitrary strings that, when changed, will force the docker\_image resource to be replaced. This can be used to rebuild an image when contents of source code folders change | `map(string)` | `{}` | no |
+| <a name="input_use_cache_from_previous_image"></a> [use\_cache\_from\_previous\_image](#input\_use\_cache\_from\_previous\_image) | If true, use the most recently pushed image in ECR as Docker cache source (cache\_from). Requires an existing ECR repo. | `bool` | `false` | no |
 | <a name="input_use_image_tag"></a> [use\_image\_tag](#input\_use\_image\_tag) | Controls whether to use image tag in ECR repository URI or not. Disable this to deploy latest image using ID (sha256:...) | `bool` | `true` | no |
 
 ## Outputs

modules/docker-build/main.tf

@@ -7,6 +7,15 @@ locals {
   ecr_repo       = var.create_ecr_repo ? aws_ecr_repository.this[0].id : var.ecr_repo
   image_tag      = var.use_image_tag ? coalesce(var.image_tag, formatdate("YYYYMMDDhhmmss", timestamp())) : null
   ecr_image_name = var.use_image_tag ? format("%v/%v:%v", local.ecr_address, local.ecr_repo, local.image_tag) : format("%v/%v", local.ecr_address, local.ecr_repo)
+
+  previous_image_from_ecr = try(data.external.latest_ecr_image[0].result.image_uri, "")
+
+  previous_image_list = (
+    var.use_cache_from_previous_image && local.previous_image_from_ecr != ""
+  ) ? [local.previous_image_from_ecr] : []
+
+  cache_from_effective = concat(var.cache_from, local.previous_image_list)
+
 }
 
 resource "docker_image" "this" {
@@ -17,7 +26,7 @@ resource "docker_image" "this" {
     dockerfile = var.docker_file_path
     build_args = var.build_args
     platform   = var.platform
-    cache_from = var.cache_from
+    cache_from = local.cache_from_effective
   }
 
   force_remove = var.force_remove
@@ -33,6 +42,17 @@ resource "docker_registry_image" "this" {
   triggers = length(var.triggers) == 0 ? { image_id = docker_image.this.image_id } : var.triggers
 }
 
+data "external" "latest_ecr_image" {
+  count = var.use_cache_from_previous_image ? 1 : 0
+
+  program = ["bash", "${path.module}/scripts/get-latest-ecr-image.sh"]
+
+  query = {
+    repository = var.ecr_repo
+    region     = data.aws_region.current.name
+  }
+}
+
 resource "aws_ecr_repository" "this" {
   count = var.create_ecr_repo ? 1 : 0
 

modules/docker-build/scripts/get-latest-ecr-image.sh

@@ -0,0 +1,37 @@
+#!/bin/bash
+
+read -r INPUT
+REPO=$(echo "$INPUT" | jq -r '.repository // empty')
+REGION=$(echo "$INPUT" | jq -r '.region // empty')
+
+if [[ -z "$REPO" || -z "$REGION" ]]; then
+  echo '{"image_uri": ""}'
+  exit 0
+fi
+
+# Check if repo exists
+if ! aws ecr describe-repositories --repository-names "$REPO" --region "$REGION" >/dev/null 2>&1; then
+  echo 'no{"image_uri": ""}'
+  exit 0
+fi
+
+# Get latest image tag
+IMAGE=$(aws ecr describe-images \
+  --repository-name "$REPO" \
+  --region "$REGION" \
+  --query 'reverse(sort_by(imageDetails, &imagePushedAt))[?imageTags]|[0].imageTags[0]' \
+  --output text 2>/dev/null || echo "")
+
+if [ -z "$IMAGE" ] || [ "$IMAGE" == "None" ]; then
+  echo '{"image_uri": ""}'
+  exit 0
+fi
+
+# Get full image URI
+URI=$(aws ecr describe-repositories \
+  --repository-names "$REPO" \
+  --region "$REGION" \
+  --query 'repositories[0].repositoryUri' \
+  --output text)
+
+echo "{\"image_uri\": \"${URI}:${IMAGE}\"}"

modules/docker-build/variables.tf

@@ -118,3 +118,9 @@ variable "cache_from" {
   type        = list(string)
   default     = []
 }
+
+variable "use_cache_from_previous_image" {
+  description = "If true, use the most recently pushed image in ECR as Docker cache source (cache_from). Requires an existing ECR repo."
+  type        = bool
+  default     = false
+}

modules/docker-build/versions.tf

@@ -14,5 +14,9 @@ terraform {
       source  = "hashicorp/null"
       version = ">= 2.0"
     }
+    external = {
+      source  = "hashicorp/external"
+      version = ">= 2.3"
+    }
   }
 }

wrappers/docker-build/main.tf

@@ -3,24 +3,25 @@ module "wrapper" {
 
   for_each = var.items
 
-  build_args                = try(each.value.build_args, var.defaults.build_args, {})
-  cache_from                = try(each.value.cache_from, var.defaults.cache_from, [])
-  create_ecr_repo           = try(each.value.create_ecr_repo, var.defaults.create_ecr_repo, false)
-  create_sam_metadata       = try(each.value.create_sam_metadata, var.defaults.create_sam_metadata, false)
-  docker_file_path          = try(each.value.docker_file_path, var.defaults.docker_file_path, "Dockerfile")
-  ecr_address               = try(each.value.ecr_address, var.defaults.ecr_address, null)
-  ecr_force_delete          = try(each.value.ecr_force_delete, var.defaults.ecr_force_delete, true)
-  ecr_repo                  = try(each.value.ecr_repo, var.defaults.ecr_repo, null)
-  ecr_repo_lifecycle_policy = try(each.value.ecr_repo_lifecycle_policy, var.defaults.ecr_repo_lifecycle_policy, null)
-  ecr_repo_tags             = try(each.value.ecr_repo_tags, var.defaults.ecr_repo_tags, {})
-  force_remove              = try(each.value.force_remove, var.defaults.force_remove, false)
-  image_tag                 = try(each.value.image_tag, var.defaults.image_tag, null)
-  image_tag_mutability      = try(each.value.image_tag_mutability, var.defaults.image_tag_mutability, "MUTABLE")
-  keep_locally              = try(each.value.keep_locally, var.defaults.keep_locally, false)
-  keep_remotely             = try(each.value.keep_remotely, var.defaults.keep_remotely, false)
-  platform                  = try(each.value.platform, var.defaults.platform, null)
-  scan_on_push              = try(each.value.scan_on_push, var.defaults.scan_on_push, false)
-  source_path               = try(each.value.source_path, var.defaults.source_path, null)
-  triggers                  = try(each.value.triggers, var.defaults.triggers, {})
-  use_image_tag             = try(each.value.use_image_tag, var.defaults.use_image_tag, true)
+  build_args                    = try(each.value.build_args, var.defaults.build_args, {})
+  cache_from                    = try(each.value.cache_from, var.defaults.cache_from, [])
+  create_ecr_repo               = try(each.value.create_ecr_repo, var.defaults.create_ecr_repo, false)
+  create_sam_metadata           = try(each.value.create_sam_metadata, var.defaults.create_sam_metadata, false)
+  docker_file_path              = try(each.value.docker_file_path, var.defaults.docker_file_path, "Dockerfile")
+  ecr_address                   = try(each.value.ecr_address, var.defaults.ecr_address, null)
+  ecr_force_delete              = try(each.value.ecr_force_delete, var.defaults.ecr_force_delete, true)
+  ecr_repo                      = try(each.value.ecr_repo, var.defaults.ecr_repo, null)
+  ecr_repo_lifecycle_policy     = try(each.value.ecr_repo_lifecycle_policy, var.defaults.ecr_repo_lifecycle_policy, null)
+  ecr_repo_tags                 = try(each.value.ecr_repo_tags, var.defaults.ecr_repo_tags, {})
+  force_remove                  = try(each.value.force_remove, var.defaults.force_remove, false)
+  image_tag                     = try(each.value.image_tag, var.defaults.image_tag, null)
+  image_tag_mutability          = try(each.value.image_tag_mutability, var.defaults.image_tag_mutability, "MUTABLE")
+  keep_locally                  = try(each.value.keep_locally, var.defaults.keep_locally, false)
+  keep_remotely                 = try(each.value.keep_remotely, var.defaults.keep_remotely, false)
+  platform                      = try(each.value.platform, var.defaults.platform, null)
+  scan_on_push                  = try(each.value.scan_on_push, var.defaults.scan_on_push, false)
+  source_path                   = try(each.value.source_path, var.defaults.source_path, null)
+  triggers                      = try(each.value.triggers, var.defaults.triggers, {})
+  use_cache_from_previous_image = try(each.value.use_cache_from_previous_image, var.defaults.use_cache_from_previous_image, false)
+  use_image_tag                 = try(each.value.use_image_tag, var.defaults.use_image_tag, true)
 }

wrappers/docker-build/versions.tf

@@ -14,5 +14,9 @@ terraform {
       source  = "hashicorp/null"
       version = ">= 2.0"
     }
+    external = {
+      source  = "hashicorp/external"
+      version = ">= 2.3"
+    }
   }
 }