Added replica init

README.md

@@ -41,18 +41,20 @@ MongoDB + Backups & Retention
 
 ## About
 
-Custom MongoDB Docker image extending `mongo:latest` with automated backup functionality. 
+Custom MongoDB Docker image extending `mongo:latest` with automated backups, retention management, and replica set configuration.
 
-Installs cron to run scheduled mongodump operations with compression and retention management, while preserving all native MongoDB server functionality.
+Includes cron-based scheduled `mongodump` operations with compression, automatic stale lock recovery on unclean shutdowns, and zero-config replica set initialization — while preserving all native MongoDB functionality.
 
-Backups can be manually triggered with: `docker --exec -t mongodb backup`
+**Manually trigger a backup:**
+docker exec -t mongodb backup
 
-To restore a backup, uncompress it and use the official `mongorestore`
+**Restore a backup:**
+Decompress the archive and use the official `mongorestore` tool.
 
 ### Environment Variables
 
 | Variable                     | Description                                                          | Default                  | Example               |
-|------------------------------|--------------------------------------------------|--------------------------|---------------|
+|------------------------------|----------------------------------------------------------------------|--------------------------|-----------------------|
 | `BACKUP_CRON`                | Cron schedule expression                                             |                          | `0 */6 * * *`         |
 | `BACKUP_DIR`                 | Directory to store backups                                           | `/data/backups`          | `/backups`            |
 | `BACKUP_DB`                  | Database to backup                                                   | `$MONGO_INITDB_DATABASE` | `admin`               |
@@ -60,6 +62,7 @@ To restore a backup, uncompress it and use the official `mongorestore`
 | `MONGO_INITDB_DATABASE`      | Default database name                                                |                          | `momentum`            |
 | `MONGO_INITDB_ROOT_USERNAME` | Root username for mongodump auth                                     |                          | `root`                |
 | `MONGO_INITDB_ROOT_PASSWORD` | Root password for mongodump auth                                     |                          | `secret`              |
+| `REPLICA`                    | Comma-separated list of replica hostnames to init/join a replica set |                          | `db1:27017,db2:27017` |
 
 ### Built With
 

docker-compose.yml

@@ -1,5 +1,5 @@
 services:
-    db:
+    db1:
         build: .
         environment:
             MONGO_INITDB_DATABASE: momentum
@@ -8,6 +8,13 @@ services:
             BACKUP_CRON: "0 2 * * *"
             BACKUP_RETENTION: "7"
             BACKUP_DIR: /data/backups
+            REPLICA: db1:27017,db2:27017 # CSV, Must match hostname
         volumes:
-            - data:/data/db
+            - data1:/data/db
             - backups:/data/backups
+    db2:
+        build: .
+        environment:
+            REPLICA: db1:27017,db2:27017 # CSV, Must match hostname
+        volumes:
+            - data2:/data/db

entrypoint.sh

@@ -15,5 +15,48 @@ if [ -f /data/db/mongod.lock ] || [ -f /data/db/WiredTiger.lock ] || [ -f /data/
     echo "Repair complete, starting normally..."
 fi
 
+if [ -n "$REPLICA" ]; then
+    # Start mongo temporarily in background with replSet enabled
+    mongod --replSet rs0 --bind_ip_all &
+    MONGO_PID=$!
+
+    # Wait for mongo to be ready
+    echo "Waiting for MongoDB to be ready..."
+    until mongosh --quiet --eval "db.runCommand({ ping: 1 })" &>/dev/null; do
+        sleep 1
+    done
+
+    # Build members array from REPLICA CSV
+    MEMBERS=""
+    INDEX=0
+    IFS=',' read -ra HOSTS <<< "$REPLICA"
+    for HOST in "${HOSTS[@]}"; do
+        [ $INDEX -gt 0 ] && MEMBERS+=","
+        MEMBERS+="{ _id: $INDEX, host: '$HOST' }"
+        INDEX=$((INDEX + 1))
+    done
+
+    # Init or reconfig replica set
+    mongosh --quiet --eval "
+        try {
+            const config = rs.conf();
+            config.members = [$MEMBERS];
+            rs.reconfig(config, { force: true });
+            print('Replica set reconfigured');
+        } catch(e) {
+            rs.initiate({ _id: 'rs0', members: [$MEMBERS] });
+            print('Replica set initiated');
+        }
+    "
+
+    # Stop the temporary mongod
+    kill $MONGO_PID
+    wait $MONGO_PID 2>/dev/null
+fi
+
+if [ -n "$REPLICA" ]; then
+    set -- mongod --replSet rs0 --bind_ip_all
+fi
+
 # Hand off to normal mongo entrypoint
 exec /usr/local/bin/docker-entrypoint.sh "$@"