Never emit an empty synchronous_standby_names list

role_scripts/10/primary/start.sh

@@ -369,7 +369,14 @@ if [[ "$STREAMING" == "synchronous" ]]; then
         done
         names=${names%,}
     fi
-    echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    # An empty list is a syntax error, not "no sync standbys" -- postgres refuses to start on
+    # 'FIRST 2 ()'. $names is empty whenever this pod is the only member it can see, e.g. a
+    # PITR restore at one replica. Empty means "wait for local flush only", so this is safe.
+    if [[ -z "${names:-}" ]]; then
+        echo "synchronous_standby_names = ''" >>/tmp/postgresql.conf
+    else
+        echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    fi
 fi
 # ref: https://superuser.com/a/246841/985093
 cat /tmp/postgresql.conf $PGDATA/postgresql.conf >"/tmp/postgresql.conf.tmp" && mv "/tmp/postgresql.conf.tmp" "$PGDATA/postgresql.conf"

role_scripts/10/standby/ha_backup_job.sh

@@ -139,7 +139,14 @@ if [[ "$STREAMING" == "synchronous" ]]; then
         done
         names=${names%,}
     fi
-    echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    # An empty list is a syntax error, not "no sync standbys" -- postgres refuses to start on
+    # 'FIRST 2 ()'. $names is empty whenever this pod is the only member it can see, e.g. a
+    # PITR restore at one replica. Empty means "wait for local flush only", so this is safe.
+    if [[ -z "${names:-}" ]]; then
+        echo "synchronous_standby_names = ''" >>/tmp/postgresql.conf
+    else
+        echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    fi
 fi
 if [[ "${SSL:-0}" == "ON" ]]; then
     echo "ssl = on" >>/tmp/postgresql.conf

role_scripts/10/standby/run.sh

@@ -203,7 +203,14 @@ if [[ "$STREAMING" == "synchronous" ]]; then
         done
         names=${names%,}
     fi
-    echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    # An empty list is a syntax error, not "no sync standbys" -- postgres refuses to start on
+    # 'FIRST 2 ()'. $names is empty whenever this pod is the only member it can see, e.g. a
+    # PITR restore at one replica. Empty means "wait for local flush only", so this is safe.
+    if [[ -z "${names:-}" ]]; then
+        echo "synchronous_standby_names = ''" >>/tmp/postgresql.conf
+    else
+        echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    fi
 fi
 if [[ "${SSL:-0}" == "ON" ]]; then
     echo "ssl = on" >>/tmp/postgresql.conf

role_scripts/10/standby/warm_stanby.sh

@@ -77,7 +77,14 @@ if [[ "$STREAMING" == "synchronous" ]]; then
         done
         names=${names%,}
     fi
-    echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    # An empty list is a syntax error, not "no sync standbys" -- postgres refuses to start on
+    # 'FIRST 2 ()'. $names is empty whenever this pod is the only member it can see, e.g. a
+    # PITR restore at one replica. Empty means "wait for local flush only", so this is safe.
+    if [[ -z "${names:-}" ]]; then
+        echo "synchronous_standby_names = ''" >>/tmp/postgresql.conf
+    else
+        echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    fi
 fi
 if [[ "${SSL:-0}" == "ON" ]]; then
     echo "ssl = on" >>/tmp/postgresql.conf

role_scripts/11/primary/start.sh

@@ -432,7 +432,14 @@ if [[ "$STREAMING" == "synchronous" ]]; then
         done
         names=${names%,}
     fi
-    echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    # An empty list is a syntax error, not "no sync standbys" -- postgres refuses to start on
+    # 'FIRST 2 ()'. $names is empty whenever this pod is the only member it can see, e.g. a
+    # PITR restore at one replica. Empty means "wait for local flush only", so this is safe.
+    if [[ -z "${names:-}" ]]; then
+        echo "synchronous_standby_names = ''" >>/tmp/postgresql.conf
+    else
+        echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    fi
 fi
 # ref: https://superuser.com/a/246841/985093
 cat /tmp/postgresql.conf $PGDATA/postgresql.conf >"/tmp/postgresql.conf.tmp" && mv "/tmp/postgresql.conf.tmp" "$PGDATA/postgresql.conf"

role_scripts/11/standby/ha_backup_job.sh

@@ -138,7 +138,14 @@ if [[ "$STREAMING" == "synchronous" ]]; then
         done
         names=${names%,}
     fi
-    echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    # An empty list is a syntax error, not "no sync standbys" -- postgres refuses to start on
+    # 'FIRST 2 ()'. $names is empty whenever this pod is the only member it can see, e.g. a
+    # PITR restore at one replica. Empty means "wait for local flush only", so this is safe.
+    if [[ -z "${names:-}" ]]; then
+        echo "synchronous_standby_names = ''" >>/tmp/postgresql.conf
+    else
+        echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    fi
 fi
 
 if [[ "${SSL:-0}" == "ON" ]]; then

role_scripts/11/standby/run.sh

@@ -207,7 +207,14 @@ if [[ "$STREAMING" == "synchronous" ]]; then
         done
         names=${names%,}
     fi
-    echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    # An empty list is a syntax error, not "no sync standbys" -- postgres refuses to start on
+    # 'FIRST 2 ()'. $names is empty whenever this pod is the only member it can see, e.g. a
+    # PITR restore at one replica. Empty means "wait for local flush only", so this is safe.
+    if [[ -z "${names:-}" ]]; then
+        echo "synchronous_standby_names = ''" >>/tmp/postgresql.conf
+    else
+        echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    fi
 fi
 if [[ "${SSL:-0}" == "ON" ]]; then
     echo "ssl = on" >>/tmp/postgresql.conf

role_scripts/11/standby/warm_stanby.sh

@@ -77,7 +77,14 @@ if [[ "$STREAMING" == "synchronous" ]]; then
         done
         names=${names%,}
     fi
-    echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    # An empty list is a syntax error, not "no sync standbys" -- postgres refuses to start on
+    # 'FIRST 2 ()'. $names is empty whenever this pod is the only member it can see, e.g. a
+    # PITR restore at one replica. Empty means "wait for local flush only", so this is safe.
+    if [[ -z "${names:-}" ]]; then
+        echo "synchronous_standby_names = ''" >>/tmp/postgresql.conf
+    else
+        echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    fi
 fi
 
 if [[ "${SSL:-0}" == "ON" ]]; then

role_scripts/12/primary/start.sh

@@ -452,7 +452,14 @@ if [[ "$STREAMING" == "synchronous" ]]; then
         done
         names=${names%,}
     fi
-    echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    # An empty list is a syntax error, not "no sync standbys" -- postgres refuses to start on
+    # 'FIRST 2 ()'. $names is empty whenever this pod is the only member it can see, e.g. a
+    # PITR restore at one replica. Empty means "wait for local flush only", so this is safe.
+    if [[ -z "${names:-}" ]]; then
+        echo "synchronous_standby_names = ''" >>/tmp/postgresql.conf
+    else
+        echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    fi
 fi
 
 # ref: https://superuser.com/a/246841/985093

role_scripts/12/standby/ha_backup_job.sh

@@ -140,7 +140,14 @@ if [[ "$STREAMING" == "synchronous" ]]; then
         done
         names=${names%,}
     fi
-    echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    # An empty list is a syntax error, not "no sync standbys" -- postgres refuses to start on
+    # 'FIRST 2 ()'. $names is empty whenever this pod is the only member it can see, e.g. a
+    # PITR restore at one replica. Empty means "wait for local flush only", so this is safe.
+    if [[ -z "${names:-}" ]]; then
+        echo "synchronous_standby_names = ''" >>/tmp/postgresql.conf
+    else
+        echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    fi
 fi
 
 if [[ "${SSL:-0}" == "ON" ]]; then

role_scripts/12/standby/run.sh

@@ -205,7 +205,14 @@ if [[ "$STREAMING" == "synchronous" ]]; then
         done
         names=${names%,}
     fi
-    echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    # An empty list is a syntax error, not "no sync standbys" -- postgres refuses to start on
+    # 'FIRST 2 ()'. $names is empty whenever this pod is the only member it can see, e.g. a
+    # PITR restore at one replica. Empty means "wait for local flush only", so this is safe.
+    if [[ -z "${names:-}" ]]; then
+        echo "synchronous_standby_names = ''" >>/tmp/postgresql.conf
+    else
+        echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    fi
 fi
 if [[ "${SSL:-0}" == "ON" ]]; then
     echo "ssl = on" >>/tmp/postgresql.conf

role_scripts/12/standby/warm_stanby.sh

@@ -86,7 +86,14 @@ if [[ "$STREAMING" == "synchronous" ]]; then
         done
         names=${names%,}
     fi
-    echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    # An empty list is a syntax error, not "no sync standbys" -- postgres refuses to start on
+    # 'FIRST 2 ()'. $names is empty whenever this pod is the only member it can see, e.g. a
+    # PITR restore at one replica. Empty means "wait for local flush only", so this is safe.
+    if [[ -z "${names:-}" ]]; then
+        echo "synchronous_standby_names = ''" >>/tmp/postgresql.conf
+    else
+        echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    fi
 fi
 if [[ "${SSL:-0}" == "ON" ]]; then
     echo "ssl = on" >>/tmp/postgresql.conf

role_scripts/13/primary/start.sh

@@ -482,7 +482,14 @@ if [[ "$STREAMING" == "synchronous" ]]; then
         done
         names=${names%,}
     fi
-    echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    # An empty list is a syntax error, not "no sync standbys" -- postgres refuses to start on
+    # 'FIRST 2 ()'. $names is empty whenever this pod is the only member it can see, e.g. a
+    # PITR restore at one replica. Empty means "wait for local flush only", so this is safe.
+    if [[ -z "${names:-}" ]]; then
+        echo "synchronous_standby_names = ''" >>/tmp/postgresql.conf
+    else
+        echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    fi
 fi
 
 # ref: https://superuser.com/a/246841/985093

role_scripts/13/standby/ha_backup_job.sh

@@ -140,7 +140,14 @@ if [[ "$STREAMING" == "synchronous" ]]; then
         done
         names=${names%,}
     fi
-    echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    # An empty list is a syntax error, not "no sync standbys" -- postgres refuses to start on
+    # 'FIRST 2 ()'. $names is empty whenever this pod is the only member it can see, e.g. a
+    # PITR restore at one replica. Empty means "wait for local flush only", so this is safe.
+    if [[ -z "${names:-}" ]]; then
+        echo "synchronous_standby_names = ''" >>/tmp/postgresql.conf
+    else
+        echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    fi
 fi
 if [[ "${SSL:-0}" == "ON" ]]; then
     echo "ssl = on" >>/tmp/postgresql.conf

role_scripts/13/standby/run.sh

@@ -209,7 +209,14 @@ if [[ "$STREAMING" == "synchronous" ]]; then
         done
         names=${names%,}
     fi
-    echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    # An empty list is a syntax error, not "no sync standbys" -- postgres refuses to start on
+    # 'FIRST 2 ()'. $names is empty whenever this pod is the only member it can see, e.g. a
+    # PITR restore at one replica. Empty means "wait for local flush only", so this is safe.
+    if [[ -z "${names:-}" ]]; then
+        echo "synchronous_standby_names = ''" >>/tmp/postgresql.conf
+    else
+        echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    fi
 fi
 
 if [[ "${SSL:-0}" == "ON" ]]; then

role_scripts/13/standby/warm_stanby.sh

@@ -80,7 +80,14 @@ if [[ "$STREAMING" == "synchronous" ]]; then
         done
         names=${names%,}
     fi
-    echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    # An empty list is a syntax error, not "no sync standbys" -- postgres refuses to start on
+    # 'FIRST 2 ()'. $names is empty whenever this pod is the only member it can see, e.g. a
+    # PITR restore at one replica. Empty means "wait for local flush only", so this is safe.
+    if [[ -z "${names:-}" ]]; then
+        echo "synchronous_standby_names = ''" >>/tmp/postgresql.conf
+    else
+        echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    fi
 fi
 
 if [[ "${SSL:-0}" == "ON" ]]; then

role_scripts/14/primary/start.sh

@@ -487,7 +487,14 @@ if [[ "$STREAMING" == "synchronous" ]]; then
         done
         names=${names%,}
     fi
-    echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    # An empty list is a syntax error, not "no sync standbys" -- postgres refuses to start on
+    # 'FIRST 2 ()'. $names is empty whenever this pod is the only member it can see, e.g. a
+    # PITR restore at one replica. Empty means "wait for local flush only", so this is safe.
+    if [[ -z "${names:-}" ]]; then
+        echo "synchronous_standby_names = ''" >>/tmp/postgresql.conf
+    else
+        echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    fi
 fi
 
 # ref: https://superuser.com/a/246841/985093

role_scripts/14/standby/ha_backup_job.sh

@@ -140,7 +140,14 @@ if [[ "$STREAMING" == "synchronous" ]]; then
         done
         names=${names%,}
     fi
-    echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    # An empty list is a syntax error, not "no sync standbys" -- postgres refuses to start on
+    # 'FIRST 2 ()'. $names is empty whenever this pod is the only member it can see, e.g. a
+    # PITR restore at one replica. Empty means "wait for local flush only", so this is safe.
+    if [[ -z "${names:-}" ]]; then
+        echo "synchronous_standby_names = ''" >>/tmp/postgresql.conf
+    else
+        echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    fi
 fi
 if [[ "${SSL:-0}" == "ON" ]]; then
     echo "ssl = on" >>/tmp/postgresql.conf

role_scripts/14/standby/run.sh

@@ -209,7 +209,14 @@ if [[ "$STREAMING" == "synchronous" ]]; then
         done
         names=${names%,}
     fi
-    echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    # An empty list is a syntax error, not "no sync standbys" -- postgres refuses to start on
+    # 'FIRST 2 ()'. $names is empty whenever this pod is the only member it can see, e.g. a
+    # PITR restore at one replica. Empty means "wait for local flush only", so this is safe.
+    if [[ -z "${names:-}" ]]; then
+        echo "synchronous_standby_names = ''" >>/tmp/postgresql.conf
+    else
+        echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    fi
 fi
 
 if [[ "${SSL:-0}" == "ON" ]]; then

role_scripts/14/standby/warm_stanby.sh

@@ -80,7 +80,14 @@ if [[ "$STREAMING" == "synchronous" ]]; then
         done
         names=${names%,}
     fi
-    echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    # An empty list is a syntax error, not "no sync standbys" -- postgres refuses to start on
+    # 'FIRST 2 ()'. $names is empty whenever this pod is the only member it can see, e.g. a
+    # PITR restore at one replica. Empty means "wait for local flush only", so this is safe.
+    if [[ -z "${names:-}" ]]; then
+        echo "synchronous_standby_names = ''" >>/tmp/postgresql.conf
+    else
+        echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    fi
 fi
 
 if [[ "${SSL:-0}" == "ON" ]]; then

role_scripts/15/primary/start.sh

@@ -490,7 +490,14 @@ if [[ "$STREAMING" == "synchronous" ]]; then
         done
         names=${names%,}
     fi
-    echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    # An empty list is a syntax error, not "no sync standbys" -- postgres refuses to start on
+    # 'FIRST 2 ()'. $names is empty whenever this pod is the only member it can see, e.g. a
+    # PITR restore at one replica. Empty means "wait for local flush only", so this is safe.
+    if [[ -z "${names:-}" ]]; then
+        echo "synchronous_standby_names = ''" >>/tmp/postgresql.conf
+    else
+        echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    fi
 fi
 
 # ref: https://superuser.com/a/246841/985093

role_scripts/15/standby/ha_backup_job.sh

@@ -142,7 +142,14 @@ if [[ "$STREAMING" == "synchronous" ]]; then
         done
         names=${names%,}
     fi
-    echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    # An empty list is a syntax error, not "no sync standbys" -- postgres refuses to start on
+    # 'FIRST 2 ()'. $names is empty whenever this pod is the only member it can see, e.g. a
+    # PITR restore at one replica. Empty means "wait for local flush only", so this is safe.
+    if [[ -z "${names:-}" ]]; then
+        echo "synchronous_standby_names = ''" >>/tmp/postgresql.conf
+    else
+        echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    fi
 fi
 if [[ "${SSL:-0}" == "ON" ]]; then
     echo "ssl = on" >>/tmp/postgresql.conf

role_scripts/15/standby/run.sh

@@ -208,7 +208,14 @@ if [[ "$STREAMING" == "synchronous" ]]; then
         done
         names=${names%,}
     fi
-    echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    # An empty list is a syntax error, not "no sync standbys" -- postgres refuses to start on
+    # 'FIRST 2 ()'. $names is empty whenever this pod is the only member it can see, e.g. a
+    # PITR restore at one replica. Empty means "wait for local flush only", so this is safe.
+    if [[ -z "${names:-}" ]]; then
+        echo "synchronous_standby_names = ''" >>/tmp/postgresql.conf
+    else
+        echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'" >>/tmp/postgresql.conf
+    fi
 fi
 
 if [[ "${SSL:-0}" == "ON" ]]; then