Prevent regular doc writes to the replication source

read_only_replication_source.sh

#!/bin/sh

# Prevent regular doc writes to the replication source. Used, for example, when
# migrating to a new instance and we want to prevent clients writing to the old
# instance by accident. Design doc writes and all doc reads can still take
# place.
#
# (`http` is the httpie client https://httpie.io/)

DB="http://adm:pass@localhost:15984"

# Reset everything
http -q delete $DB/old
http -q delete $DB/new
http -q delete $DB/_replicator
http -q put $DB/_replicator

set -xe

http -b put $DB/old
http -b put $DB/old/old1 a=b

# Create a VDU to forbid all regular doc writes. Instead of null could emit a
# message where the new instance is.
http -b put $DB/old/_design/rovdu \
  validate_doc_update:='"function(newDoc, oldDoc, userCtx){throw({forbidden: null});}"'


# Make sure not to replicate the VDU to the target
http -b put $DB/_replicator/old2new \
  source=$DB/old \
  target=$DB/new \
  selector:='{"$not": {"_id": "_design/rovdu"}}' \
  continuous:='true' \
  create_target:='true'


# Replication jobs have a random 5 second startup jitter
sleep 6

http -b get $DB/new/_all_docs

# Let's try writing a doc to the source. This should fail with non-0 exit code
http --check-status put $DB/old/old2 c=d