I have docker compose file as

---
version: '3.7'
services:
  myapi:
    image: tiangolo/uwsgi-nginx-flask:python3.7
    env_file: apivars.env
    logging:
      driver: syslog
      options:
        syslog-address: "udp://127.0.0.1:514"
        tag: tags
        labels: labels
    ports:
      - "8080:80"
    deploy:
      placement:
        constraints:
          - node.role != manager
      mode: replicated
      replicas: 32
      update_config:
        parallelism: 4
        delay: 5s
        order: start-first
...

I have load balancer which will redirect request to this swarm manager.

My understanding is, if I hit www.myapi.com, it will got to LoadBalancer and then request will go to swarm manager, then swarm manager send that request to on of the 32 replicas.

Now issue is, LoadBalancer logs report some of the 502 errors.

# head -n1 /var/log/haproxy.log
Apr 28 09:35:28 localhost haproxy[43117]: 172.19.9.1:50220 [28/Apr/2020:09:35:08.549] main~ API_Production/swarmnode5 0/0/1/19952/19953 502 309 - - ---- 97/97/10/1/0 0/0 "GET /v2/students/?includeFields=name,id&per_page=1000&page=88 HTTP/1.1"

I have to check its reaching to swarm manager or swarmnode5 ?

I check the logs for nginx, but its not report any 502 errors. There are some exceptions, but not sure if exception is there in code, then why nginx not logs that api call and response?