Made replication optional

Author: djthorpe

README.md

@@ -11,13 +11,14 @@ Replacing the `DOCKER_REPO` with the repository you want to push the image to.
 
 ## Environment variables
 
-The image can be run as a primary or replica, depending on the environment variables passed on the
+The image can be run as a standalone instance, primary, or replica, depending on the environment variables passed on the
 docker command line:
 
 * `POSTGRES_REPLICATION_PRIMARY`: **Required for replica** The host and port that the replica will use
   to connect to the primary, in the form `host=<hostname> port=5432`. When not set,
-  the instance role is a primary.
-* `POSTGRES_REPLICATION_PASSWORD`: **Required**: The password for the `POSTGRES_REPLICATION_USER`.
+  the instance role is a primary or standalone.
+* `POSTGRES_REPLICATION_PASSWORD`: **Required for replication**: The password for the `POSTGRES_REPLICATION_USER`.
+  If not set, replication is disabled and the instance runs as a standalone server.
 * `POSTGRES_REPLICATION_USER`: **Default is `replicator`**: The user that the replica will use to connect to the primary.
 * `POSTGRES_REPLICATION_SLOT`: **Default is `replica1`**: The replication slot for each replica.
   On the primary, this is a comma-separated list of replication slots. On a replica, this is the name
@@ -34,6 +35,22 @@ docker command line:
 * `POSTGRES_SSL_CA`: **Optional**: The SSL CA certificate file location for client certificate verification.
   Only used when `POSTGRES_SSL_CERT` and `POSTGRES_SSL_KEY` are set.
 
+## Running a standalone server
+
+Example of running a standalone PostgreSQL instance without replication:
+
+```bash
+docker volume create postgres-data
+docker run \
+  --rm --name postgres \
+  -e POSTGRES_PASSWORD="postgres" \
+  -p 5432:5432 \
+  -v postgres-data:/var/lib/postgresql/data \
+  ghcr.io/mutablelogic/docker-postgres:17-bookworm
+```
+
+This gives you PostgreSQL with `pg_stat_statements` pre-loaded, plus PostGIS and pgvector available.
+
 ## Running a Primary server
 
 Example of running a primary instance, with two replication slots.

scripts/10_primary.sh

@@ -1,5 +1,5 @@
 #!/bin/bash
-# Script runs on a primary instance to set up replication slots
+# Script runs on a primary instance to set up replication slots and pg_stat_statements
 # The primary instance should be started before the replicas
 set -e
 
@@ -9,12 +9,19 @@ if [ ! -z "${POSTGRES_REPLICATION_PRIMARY}" ]; then
     exit 0
 fi
 
-# Validate required environment variables
+CONF="${PGDATA}/postgresql.conf"
+
+# Enable pg_stat_statements extension (always)
+sed -i -e"s/^#shared_preload_libraries.*$/shared_preload_libraries = 'pg_stat_statements'/" ${CONF}
+echo "pg_stat_statements.max = 1000" >> ${CONF}
+
+# Skip replication setup if no password is set
 if [ -z "${POSTGRES_REPLICATION_PASSWORD}" ]; then
-    echo "POSTGRES_REPLICATION_PASSWORD needs to be set."
-    exit 1
+    echo "No POSTGRES_REPLICATION_PASSWORD set, skipping replication setup."
+    exit 0
 fi
 
+# Validate replication environment variables
 if [ -z "${POSTGRES_REPLICATION_USER}" ]; then
     echo "POSTGRES_REPLICATION_USER needs to be set."
     exit 1
@@ -49,14 +56,9 @@ EOSQL
 done
 
 # Set configuration for replication
-CONF="${PGDATA}/postgresql.conf"
 sed -i -e"s/^#wal_level.*$/wal_level = replica/" ${CONF}
 sed -i -e"s/^#max_wal_senders.*$/max_wal_senders = 10/" ${CONF}
 sed -i -e"s/^#max_replication_slots.*$/max_replication_slots = 10/" ${CONF}
 
-# Enable pg_stat_statements extension
-sed -i -e"s/^#shared_preload_libraries.*$/shared_preload_libraries = 'pg_stat_statements'/" ${CONF}
-echo "pg_stat_statements.max = 1000" >> ${CONF}
-
 # Add a replication user to pg_hba.conf
 echo "host replication ${POSTGRES_REPLICATION_USER} all scram-sha-256" >> "${PGDATA}/pg_hba.conf"