diff --git a/Dockerfile b/Dockerfile
new file mode 100644
index 0000000..0ab80d8
--- /dev/null
+++ b/Dockerfile
@@ -0,0 +1,6 @@
+FROM postgres:15
+
+COPY docker-entrypoint-initdb.d/* /docker-entrypoint-initdb.d/
+
+RUN mkdir /wal_archive
+VOLUME /wal_archive
diff --git a/README.md b/README.md
index 52ca1d2..0c8825c 100644
--- a/README.md
+++ b/README.md
@@ -1,2 +1,85 @@
-# postgres15replicate
+# postgres15
+
+Implement automatic primary and standby
+
+## Primary
+
+Example `compose.yaml` for **primary** instance.
+
+```yaqml
+services:
+  db:
+    image: pendragon.zone/docker/postgres15replicate
+    restart: unless-stopped
+    shm_size: 128mb
+    environment:
+      POSTGRES_PASSWORD: ${DB_ROOT_PASSWORD}
+      REPLICATOR_PASSWORD: ${REPLICATOR_PASSWORD}
+      MAX_CONNECTIONS: "400"
+
+    network_mode: bridge
+    ports:
+      - 5432:5432
+
+    volumes:
+      - data:/var/lib/postgresql/data
+      - /docker/postgres_wal:/wal_archive
+
+volumes:
+  data:
+```
+
+- Volume `/wal_archive` **must** be mapped to a location available by **all** replication participants.
+
+- `DB_ROOT_PASSWORD` _required_, must be the same for all replication participants.
+
+- `REPLICATOR_PASSWORD` _required_, must be the same for all replication participants.
+
+- `UPSTREAM` **must not** be set for **primary** instance.
+
+- `WAL_ARCHIVE` _default: `/wal_archive`_ use different location for write-ahead-logs.
+
+- `TRIGGER_FILE` _default: `i_am_primary`_, name of the file that promotes a standby instance to primary instance, if it exists in directory `/var/lib/postgresql/data`.
+
+- `WAL_KEEP_SIZE` _default: `1GB`_
+
+- `REPLICATOR_NAME` _default: `replicator`_ name of user for replication.
+
+- `MAX_CONNECTIONS` _optional_, change default value of `max_connections` configuration value.
+
+
+## Standby
+
+Example `compose.yaml` for **standby** instance.
+
+```yaqml
+services:
+  db:
+    image: pendragon.zone/docker/postgres15replicate
+    restart: unless-stopped
+    shm_size: 128mb
+    environment:
+      POSTGRES_PASSWORD: ${DB_ROOT_PASSWORD}
+      REPLICATOR_PASSWORD: ${REPLICATOR_PASSWORD}
+      UPSTREAM: ${UPSTREAM}
+
+    network_mode: bridge
+    ports:
+      - 5432:5432
+
+    volumes:
+      - data:/var/lib/postgresql/data
+      - /docker/postgres_wal:/wal_archive
+
+volumes:
+  data:
+```
+
+- Volume `/wal_archive` **must** be mapped to a location available by **all** replication participants.
+
+- `DB_ROOT_PASSWORD` _required_, must be the same for all replication participants.
+
+- `REPLICATOR_PASSWORD` _required_, must be the same for all replication participants.
+
+- `UPSTREAM` _required_, name of the node to replicate from. Can either be **primary** or a different **standby** instance.
 
diff --git a/docker-entrypoint-initdb.d/00-main.sh b/docker-entrypoint-initdb.d/00-main.sh
new file mode 100755
index 0000000..b1c990b
--- /dev/null
+++ b/docker-entrypoint-initdb.d/00-main.sh
@@ -0,0 +1,38 @@
+#!/usr/bin/env bash
+
+# the variable UPSTREAM indicates that a standby instance is requested, otherwise this is primary
+if [[ -z $UPSTREAM ]]; then
+
+  # ensure required entries in configuration
+  # shellcheck disable=SC2129
+  echo "archive_command      = 'cp %p ${WAL_ARCHIVE:-/wal_archive}/%f'" >> /var/lib/postgresql/data/postgresql.conf
+  echo "archive_mode         = on" >> /var/lib/postgresql/data/postgresql.conf
+  echo "hot_standby          = on" >> /var/lib/postgresql/data/postgresql.conf
+  echo "promote_trigger_file = '/var/lib/postgresql/data/${TRIGGER_FILE:-i_am_primary}'" >> /var/lib/postgresql/data/postgresql.conf
+  echo "wal_keep_size        = ${WAL_KEEP_SIZE:-1GB}" >> /var/lib/postgresql/data/postgresql.conf
+  echo "wal_level            = replica" >> /var/lib/postgresql/data/postgresql.conf
+  # ensure required entries in hba
+  echo "host  replication  ${REPLICATOR_NAME:-replicator}  all  md5" >> /var/lib/postgresql/data/pg_hba.conf
+  # create user for replication
+  psql -c "CREATE USER ${REPLICATOR_NAME:-replicator} WITH REPLICATION ENCRYPTED PASSWORD '${REPLICATOR_PASSWORD}'; GRANT CONNECT ON DATABASE postgres TO ${REPLICATOR_NAME:-replicator}"
+
+
+  # process selected tweaks
+  if [[ -n $MAX_CONNECTIONS ]]; then
+      echo "max_connections      = ${MAX_CONNECTIONS}" >> /var/lib/postgresql/data/postgresql.conf
+  fi
+
+else
+# this is a standby
+  source /usr/local/bin/docker-entrypoint.sh
+
+  docker_temp_server_stop
+
+  rm -rf /var/lib/postgresql/data/*
+
+  OLD_PGPASSWORD=$PGPASSWORD
+  export PGPASSWORD=$REPLICATOR_PASSWORD
+  pg_basebackup -h "${UPSTREAM}" -U "${REPLICATOR_NAME:-replicator}" -D "${PGDATA}" -Fp -Xs -P -R
+  export PGPASSWORD=$OLD_PGPASSWORD
+
+fi