feat!: add sample cdc

samples/postgres-cdc/Dockerfile

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+FROM postgres:12.16
+
+RUN apt-get update
+RUN apt-get install -y postgresql-12-wal2json
+RUN apt-get install -y redis-tools
+
+COPY startup.sh .
+
+ENV CDC_DB_NAME=CDC_DB_NAME
+
+ENV REDIS_HOST=REDIS_HOST
+ENV REDIS_PORT=6379
+ENV REDIS_CHANNEL=REDIS_CHANNEL
+
+USER postgres
+CMD ./startup.sh

samples/postgres-cdc/README.md

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+This is a working CDC example for a local Postgres 12 / Redis.
+It relies on wal2json for change notifications, see https://github.com/eulerto/wal2json.
+It uses redis-cli to publish the notifications.
+
+Demo usage:
+
+- the CDC'ed database must pre-exist, it should first be created as follows
+- run `cd cdc`
+- run `docker run -p 5432:5432 -v ./postgres-data:/var/lib/postgresql/data -e POSTGRES_USER=postgres -e POSTGRES_PASSWORD=postgres postgres:12.16`
+- using a postgresql client, create the 'test_db' database and a table
+- Ctrl-C the docker container started above
+- now run `docker compose up -d`
+- checking configuration:
+
+ - from docker desktop, open a terminal to redis container
+ - from that terminal, run `redis-cli SUBSCRIBE test_db_changes`
+ - using a postgresql client, perform some inserts, updates or deletes in the 'test_db' database
+
+Real usage:
+
+- you need to configure the env variables of the postgres service in the docker-compose.yml file
+- the database name should be set to the messages repository name configured for the mediator

samples/postgres-cdc/docker-compose.yml

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+version: '3'
+
+services:
+ postgres:
+ build: .
+ image: pgsql-cdc/latest
+ container_name: cdc-pgsql
+ platform: linux/amd64
+ ports:
+ - 5432:5432
+ volumes:
+ - ./postgres-data:/var/lib/postgresql/data
+ environment:
+ - POSTGRES_USER=postgres
+ - POSTGRES_PASSWORD=postgres
+ - CDC_DB_NAME=test_db
+ - REDIS_HOST=host.docker.internal
+ - REDIS_PORT=6379
+ - REDIS_CHANNEL=test_db_changes
+
+ redis:
+ image: redis:7.2.3
+ container_name: cdc-redis
+ platform: linux/amd64
+ ports:
+ - 6379:6379

samples/postgres-cdc/startup.sh

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+#!/bin/bash
+
+# run postgres in the background so we can run pg_recvlogical
+postgres -c wal_level=logical -c max_wal_senders=1 -c shared_preload_libraries=wal2json &
+# ensure postgres is fully initialized before running pg_recvlogical
+sleep 10s
+# create replication slot if required
+pg_recvlogical -d test_db --slot ${CDC_DB_NAME}_slot --create-slot --if-not-exists -P wal2json
+# need a function for publishing otherwise bash shouts
+publish_to_redis() {
+ redis-cli -h $REDIS_HOST -p $REDIS_PORT PUBLISH $REDIS_CHANNEL $1
+}
+# listen to replication messages and publish them to redis
+pg_recvlogical -d ${CDC_DB_NAME} --slot ${CDC_DB_NAME}_slot --start -o pretty-print=0 -f - | while read message; do publish_to_redis $message ; done
+# uncomment the following if you comment the previous to keep the container running
+# tail -f /dev/null