chore: added BUILD.md and Makefile

Signed-off-by: Gabriele Bartolini <[email protected]>

Author: gbartolini

BUILD.md

@@ -0,0 +1,86 @@
+# Building Postgres Extensions Container Images for CloudNativePG
+
+This guide explains how to build Postgres extensions operand images for
+[CloudNativePG](https://cloudnative-pg.io) using
+[Docker Bake](https://docs.docker.com/build/bake/) together with a
+[GitHub Actions workflow](.github/workflows/bake.yml).
+
+Although it is not necessary, we recommend you use
+[GNU Make](https://www.gnu.org/software/make/) to build the images locally as
+outlined below.
+
+## Prerequisites
+
+This project depends on
+[`postgres-containers`](https://github.com/cloudnative-pg/postgres-containers).
+
+Before you begin, ensure that you have met the
+[prerequisites](https://github.com/cloudnative-pg/postgres-containers/blob/main/BUILD.md#prerequisites)
+defined by that project, which primarily include:
+
+1.  **Docker:** Must be installed and running.
+2.  **Docker Command Line:** The `docker` command must be executable.
+3.  **Docker Buildx:** The `docker buildx` plugin must be available.
+4.  **Docker Context:** A valid Docker context must be configured.
+
+---
+
+## Usage and Targets
+
+The `Makefile` dynamically discovers all subdirectories that contain a
+`metadata.hcl` file (e.g., `./pgvector/metadata.hcl`) and creates individual
+build targets for each project.
+
+### 1. Build Configuration Check (Dry Run)
+
+To verify the configuration (running `docker buildx bake --check`) for all
+projects without building or pulling layers:
+
+```bash
+make check
+```
+
+### 2. Build All Projects
+
+To check prerequisites and build all discovered projects:
+
+```bash
+make
+# or
+make all
+````
+
+### 3. Build a Specific Project
+
+To build a single project (e.g., the directory named `pgvector`):
+
+```bash
+make pgvector
+```
+
+### 4. Push All Images
+
+To build all images and immediately push them to the configured registry:
+
+```bash
+make push
+```
+
+### 5. Check Prerequisites Only
+
+To verify that Docker and Buildx are correctly installed and configured:
+
+```bash
+make prereqs
+```
+
+### 6. Dry Run Mode
+
+To see the commands that would be executed without running the actual `docker
+buildx bake` command, set the `DRY_RUN` flag:
+
+```bash
+make DRY_RUN=true
+# or
+make pgvector DRY_RUN=true
+```

Makefile

@@ -0,0 +1,69 @@
+.SUFFIXES:
+
+# Find all directories containing metadata.hcl
+FILES := $(shell find . -type f -name metadata.hcl)
+DIRS  := $(patsubst %/,%,$(patsubst ./%,%,$(dir $(FILES))))
+
+.PHONY: all clean check prereqs $(DIRS)
+
+# Colours
+GREEN := \033[0;32m
+BLUE  := \033[0;34m
+RED   := \033[0;31m
+NC    := \033[0m
+
+# Dry run flag
+DRY_RUN ?= false
+
+# --------------------------
+# Prerequisite checks
+# --------------------------
+prereqs:
+	@echo -e "$(BLUE)Checking prerequisites...$(NC)"
+	@command -v docker >/dev/null 2>&1 || { echo -e "$(RED)Docker is not installed.$(NC)"; exit 1; }
+	@docker --version >/dev/null 2>&1 || { echo -e "$(RED)Cannot run docker command.$(NC)"; exit 1; }
+	@docker buildx version >/dev/null 2>&1 || { echo -e "$(RED)Docker Buildx not available.$(NC)"; exit 1; }
+	@docker context inspect >/dev/null 2>&1 || { echo -e "$(RED)Docker context not configured.$(NC)"; exit 1; }
+	@echo -e "$(GREEN)All prerequisites satisfied!$(NC)"
+
+# --------------------------
+# Dry-run or verification
+# --------------------------
+check: prereqs
+	@echo -e "$(BLUE)Performing bake --check for all projects...$(NC)"
+	@$(foreach dir,$(DIRS), \
+		echo -e "$(BLUE)[CHECK] $dir$(NC)"; \
+		docker buildx bake -f $(dir)/metadata.hcl -f docker-bake.hcl --check; \
+	)
+
+# --------------------------
+# Push all images
+# --------------------------
+push: all
+	@echo -e "$(BLUE)Performing bake --push for all projects...$(NC)"
+	@$(foreach dir,$(DIRS), \
+		echo -e "$(BLUE)[PUSH] $dir$(NC)"; \
+		if [ "$(DRY_RUN)" = "true" ]; then \
+			echo -e "$(GREEN)[DRY RUN] docker buildx bake -f $(dir)/metadata.hcl -f docker-bake.hcl --push$(NC)"; \
+		else \
+			docker buildx bake -f $(dir)/metadata.hcl -f docker-bake.hcl --push; \
+		fi; \
+	)
+
+# --------------------------
+# Build targets
+# --------------------------
+all: prereqs $(DIRS)
+	@echo -e "$(GREEN)======================================================$(NC)"
+	@echo -e "$(GREEN)Build successful for all projects: $(DIRS)$(NC)"
+	@echo -e "$(GREEN)======================================================$(NC)"
+
+# Per-project build
+$(DIRS): %: %/metadata.hcl
+	@echo -e "$(BLUE)--- Starting Docker Buildx Bake for target: $@ ---$(NC)"
+ifeq ($(DRY_RUN),true)
+	@echo -e "$(GREEN)[DRY RUN] docker buildx bake -f $@/metadata.hcl -f docker-bake.hcl$(NC)"
+else
+	docker buildx bake -f $@/metadata.hcl -f docker-bake.hcl
+endif
+	@echo -e "$(GREEN)--- Successfully built $@ ---$(NC)"

README.md

@@ -8,6 +8,8 @@ container images** containing PostgreSQL extensions supported by
 integrate seamlessly with the [`image volume extensions` feature](https://cloudnative-pg.io/documentation/current/imagevolume_extensions/)
 in CloudNativePG.
 
+For detailed instructions on building the images, see the [BUILD.md file](BUILD.md).
+
 ---
 
 ## Requirements