DEV_NOTE.md

DEV NOTE

list myapp services

docker exec vps1 systemctl list-units | grep myapp

example list services output

root@vps1:/# systemctl list-units | grep myapp
  myapp@3000.service                       loaded active     running   crane managed: myapp instance on port 3000
  myapp@3001.service                       loaded active     running   crane managed: myapp instance on port 3001
  system-myapp.slice                       loaded active     active    Slice /system/myapp

see myapp systemd unit file

docker exec vps1 cat /etc/systemd/system/myapp@.service

stop myapp service

docker exec vps1 systemctl stop myapp@3000.service

Testing services can connect to each other

# myapp → hits http://myapp2 (via /etc/hosts)
curl -w "\n" -L -k -i myapp.localhost/curl?to=myapp2


# myapp2 → hits http://myapp
curl -w "\n" -L -k -i myapp2.localhost/curl?to=myapp

fix can't ssh into vps

docker exec vps1 rm -f /run/nologin && docker exec vps1 systemctl restart systemd-user-sessions.service

Get myapp logs on port 3000

journalctl -xeu myapp@3000.service

Get myapp2 logs on port 4000

journalctl -xeu myapp2@4000.service

Patroni & Etcd Debug Commands

check etcd logs journalctl

docker exec vps1 journalctl -xeu etcd -n 100 -ocat

check patroni logs journalctl

docker exec vps1 journalctl -xeu patroni.service -n 100 -ocat

check summarize_wal on

docker exec vps1 sudo -u postgres psql -t -c "select name, setting, source, sourcefile, sourceline from pg_settings where name = 'summarize_wal';"

DEBUG slow assert_postgres_cluster_healthy

Are replication connections visible?

psql -U postgres -c "SELECT pid, usename, application_name, client_addr, state, sent_lsn, write_lsn, flush_lsn, replay_lsn, sync_state FROM pg_stat_replication;"

Check replication slots (if used — slots can block or stall)

psql -U postgres -c "SELECT slot_name, active, restart_lsn, pg_size_pretty(pg_wal_lsn_diff(pg_current_wal_lsn(), restart_lsn)) AS lag FROM pg_replication_slots;"

Confirm wal_senders headroom

psql -U postgres -c "SHOW max_wal_senders;"

Compare against current count from pg_stat_replication