Pool connect ignores DNS ttl

[alexmac]

• asyncpg version: 0.14
• PostgreSQL version: 9.5/9.6
• Do you use a PostgreSQL SaaS? If so, which? Can you reproduce
  the issue with a local PostgreSQL install?: Using AWS RDS
• Python version: 3.6
• Platform: Linux in docker
• Do you use pgbouncer?: Not in this instances
• Did you install asyncpg with pip?: yes
• If you built asyncpg locally, which version of Cython did you use?:
• Can the issue be reproduced under both asyncio and
  uvloop?: We only use asyncio

After performing a failover/reboot of an AWS RDS instance asyncpg does not appear to reconnect gracefully - it looks like the code in Pool caches the IP of the PG instance after dns resolution and does not respect whatever TTL we might have set on the cname that points at our master: https://.com/MagicStack/asyncpg/blob/master/asyncpg/pool.py#L133

[egalpin]

See #253 (which supersedes #249), which attempts to address this exact issue by tracking the consecutive number of exceptions that a connection has incurred. After the max is reached, the connection is closed so that a new one can be added to the pool. We've found this to have effectively mitigated our failover issues (also using RDS).

You can install it by adding the following to your requirements.txt or as part of a build process (also requires Cython):
(requirements.txt)

git+https://.com/egalpin/asyncpg.git@add_max_exceptions_to_pool#egg=asyncpg

(plain pip)

pip install git+https://.com/egalpin/asyncpg.git@add_max_exceptions_to_pool#egg=asyncpg

[egalpin]

Though, after reading the code you pointed to more closely, it may be better handled by updating the connection logic to not cache (or, optionally so) the resolved address

[egalpin]

See specifically this commit which will cause a pool to cycle through your provided hosts again should a connection end up being closed due to too many consecutive exceptions

[elprans]

asyncpg does not perform any name resolution itself, Connection._addr and Pool._working_addr contain the host string as it was passed to connect().