snapshot: override_constraint (#411)

#410

snapshot/docker_service_create.sh

@@ -63,10 +63,19 @@ if [[ -z $snapshot_storage_node ]]; then
   MOUNT_OPT="--mount type=bind,source=$MOUNT_SRC,destination=/snapshot"
 fi
 
-constraint="node.hostname==$HOST"
-if [ $( echo "${chain_name}" | egrep -c "archive" ) -eq 0 ]; then
-  # if pruned node, place on node with cosmosia.snapshot.pruned label, see https://github.com/notional-labs/cosmosia/issues/375
-	constraint="node.labels.cosmosia.snapshot.pruned==true"
+
+# use override constraint if found
+override_constraint=$(docker node ls -f node.label=cosmosia.snapshot.${chain_name}=true | tail -n +2 |awk '{print $2}')
+if [[ -z $override_constraint ]]; then
+  echo "No override_constraint found"
+  constraint="node.hostname==$HOST"
+  if [ $( echo "${chain_name}" | egrep -c "archive" ) -eq 0 ]; then
+    # if pruned node, place on node with cosmosia.snapshot.pruned label, see https://github.com/notional-labs/cosmosia/issues/375
+    constraint="node.labels.cosmosia.snapshot.pruned==true"
+  fi
+else
+  echo "Found override_constraint=${override_constraint}"
+  constraint="node.labels.cosmosia.snapshot.${chain_name}==true"
 fi
 
 echo "constraint= ${constraint}"