Recently, our PHP web app became unavailable for a few minutes since one of our Memcached nodes died (we use Memcachier as a Memcached provider).
This was our user.ini configuration (Heroku uses user.ini as a place where you define your configuration), which worked, but apparently didn't support failover:
session.save_handler=memcached
session.save_path=${MEMCACHIER_SERVERS} # I understand this is redundant, but I just kept it as-is because I didn't write the original user.ini
session.save_path="PERSISTENT=SFSESSID ${MEMCACHIER_SERVERS}"
session.gc_maxlifetime=1209600
session.gc_probability=1
memcached.sess_binary=1
memcached.sess_sasl_username=${MEMCACHIER_USERNAME}
memcached.sess_sasl_password=${MEMCACHIER_PASSWORD}
Our new user.ini configuration, which is aimed to provide failover capability
session.save_handler=memcached
session.save_path="PERSISTENT=SFSESSID ${MEMCACHIER_SERVERS}"
session.gc_maxlifetime=1209600
session.gc_probability=1
memcached.sess_sasl_username=${MEMCACHIER_USERNAME}
memcached.sess_sasl_password=${MEMCACHIER_PASSWORD}
memcached.sess_binary=1
memcached.sess_number_of_replicas=1
# I also tried memcached.sess_consistent_hash=1, to no avail
The MEMCACHIER_SERVERS env var looks like this: 123.45678.us-east-1.heroku.prod.memcachier.com:11211,123.45678.us-east-1.heroku.prod.memcachier.com:11211. I think this means we have 2 nodes.
The problem we are getting with the new configuration are timeouts, and lots of errors regarding PHP session functions (session_start(), session_write_close()).
Why is that happening?
Remember, we're not using Memcached inside our PHP code at all, but only as our session storage engine.
I did try contacting Memcachier support, but the customer representative could only provide recommended PHP code (which we don't need).
Since the bounty expired and the question will get closed soon, I'm gonna go ahead with @jdotjdot's suggestion and switch from Memcachier to MemcachedCloud addon.