I am designing a program that will send messages (Client PC) to a Linux VM (Ubuntu) that will house the docker containers (Docker Host), where each container will have a program that will receive the message and then respond to the client PC through UDP and potentially TCP protocols where I specify the port.

Designing it for a single container worked perfectly with no issues, however, if I want to make another container then it will cause an issue with the connection to that same port. Hence, I found this Link (How to Expose Multiple Containers On the Same Port) and decided to go for Nginx and set it up on the Linux VM. So I went with the following settings:

sudo cat /etc/nginx/nginx.conf
user www-data;
worker_processes auto;
pid /run/nginx.pid;
error_log /var/log/nginx/error.log debug;
include /etc/nginx/modules-enabled/*.conf;

events {
    worker_connections 768;
    # multi_accept on;
}

# TCP and UDP Load Balancing
stream {
    # TCP Load Balancing
    upstream tcp_backend {
        server 172.17.0.2:8889;  # Container 1 (TCP)
        server 172.17.0.3:8890;  # Container 2 (TCP)
        server 172.17.0.4:8891;  # Container 3 (TCP)
    }

    server {
        listen 8888;            # TCP load balancer listens on port 8888
        proxy_pass tcp_backend; # Forward requests to the TCP backend
        proxy_timeout 20s;      # Timeout for proxied requests
    }

    # UDP Load Balancing
    upstream udp_backend {
        server 172.17.0.2:8889;  # Container 1 (UDP)
        server 172.17.0.3:8890;  # Container 2 (UDP)
        server 172.17.0.4:8891;  # Container 3 (UDP)
    }

    server {
        listen 8888 udp;        # UDP load balancer listens on port 8888
        proxy_pass udp_backend; # Forward requests to the UDP backend
        proxy_timeout 20s;      # Timeout for proxied requests
    }
}

http {
    ##
    # Basic Settings
    ##

    sendfile on;
    tcp_nopush on;
    types_hash_max_size 2048;
    # server_tokens off;

    # server_names_hash_bucket_size 64;
    # server_name_in_redirect off;

    include /etc/nginx/mime.types;
    default_type application/octet-stream;

    ##
    # SSL Settings
    ##

    ssl_protocols TLSv1 TLSv1.1 TLSv1.2 TLSv1.3; # Dropping SSLv3, ref: POODLE
    ssl_prefer_server_ciphers on;

    ##
    # Logging Settings
    ##

    access_log /var/log/nginx/access.log;

    ##
    # Gzip Settings
    ##

    gzip on;

    # gzip_vary on;
    # gzip_proxied any;
    # gzip_comp_level 6;
    # gzip_buffers 16 8k;
    # gzip_http_version 1.1;
    # gzip_types text/plain text/css application/json application/javascript text/xml application/xml application/xml+rss text/javascript;

    ##
    # Virtual Host Configs
    ##

    include /etc/nginx/conf.d/*.conf;
    include /etc/nginx/sites-enabled/*;
}

#mail {
#   # See sample authentication script at:
#   # http://wiki.nginx.org/ImapAuthenticateWithApachePhpScript
#
#   # auth_http localhost/auth.php;
#   # pop3_capabilities "TOP" "USER";
#   # imap_capabilities "IMAP4rev1" "UIDPLUS";
#
#   server {
#       listen     localhost:110;
#       protocol   pop3;
#       proxy      on;
#   }
#
#   server {
#       listen     localhost:143;
#       protocol   imap;
#       proxy      on;
#   }
#}

So I can see communication in the Nginx as follows:

sudo tcpdump -i any -n port 8887 or port 8888
tcpdump: data link type LINUX_SLL2
tcpdump: verbose output suppressed, use -v[v]... for full protocol decode
listening on any, link-type LINUX_SLL2 (Linux cooked v2), snapshot length 262144 bytes
11:15:12.874895 eth0  In  IP 192.168.1.2.63075 > 192.168.1.3.8887: UDP, length 315
11:15:12.875338 eth0  In  IP 192.168.1.2.63075 > 172.17.0.1.8887: UDP, length 315
11:15:13.463923 docker0 Out IP 172.17.0.1.32893 > 172.17.0.2.8888: UDP, length 315
11:15:13.463928 vethf560a7c Out IP 172.17.0.1.32893 > 172.17.0.2.8888: UDP, length 315
11:15:27.752880 eth0  In  IP 192.168.1.2.63075 > 192.168.1.3.8887: UDP, length 315
11:15:27.753394 eth0  In  IP 192.168.1.2.63075 > 172.17.0.1.8887: UDP, length 315
11:15:28.457848 docker0 Out IP 172.17.0.1.32893 > 172.17.0.2.8888: UDP, length 315
11:15:28.457852 vethf560a7c Out IP 172.17.0.1.32893 > 172.17.0.2.8888: UDP, length 315
11:15:42.764085 eth0  In  IP 192.168.1.2.63075 > 192.168.1.3.8887: UDP, length 315
11:15:42.764804 eth0  In  IP 192.168.1.2.63075 > 172.17.0.1.8887: UDP, length 315
11:15:43.458021 docker0 Out IP 172.17.0.1.32893 > 172.17.0.2.8888: UDP, length 315
11:15:43.458026 vethf560a7c Out IP 172.17.0.1.32893 > 172.17.0.2.8888: UDP, length 315
11:15:43.520311 vethf560a7c P   IP 172.17.0.2.47084 > 172.17.0.1.8888: Flags [S], seq 1001230011, win 32120, options [mss 1460,sackOK,TS val 2027316222 ecr 0,nop,wscale 7], length 0
11:15:43.520320 docker0 In  IP 172.17.0.2.47084 > 172.17.0.1.8888: Flags [S], seq 1001230011, win 32120, options [mss 1460,sackOK,TS val 2027316222 ecr 0,nop,wscale 7], length 0
11:15:43.520335 docker0 Out IP 172.17.0.1.8888 > 172.17.0.2.47084: Flags [S.], seq 2759787398, ack 1001230012, win 31856, options [mss 1460,sackOK,TS val 312322409 ecr 2027316222,nop,wscale 7], length 0
11:15:43.520338 vethf560a7c Out IP 172.17.0.1.8888 > 172.17.0.2.47084: Flags [S.], seq 2759787398, ack 1001230012, win 31856, options [mss 1460,sackOK,TS val 312322409 ecr 2027316222,nop,wscale 7], length 0
11:15:43.520348 vethf560a7c P   IP 172.17.0.2.47084 > 172.17.0.1.8888: Flags [.], ack 1, win 251, options [nop,nop,TS val 2027316222 ecr 312322409], length 0
11:15:43.520350 docker0 In  IP 172.17.0.2.47084 > 172.17.0.1.8888: Flags [.], ack 1, win 251, options [nop,nop,TS val 2027316222 ecr 312322409], length 0
11:15:43.520504 docker0 Out IP 172.17.0.1.40166 > 172.17.0.2.8888: Flags [S], seq 1240504208, win 32120, options [mss 1460,sackOK,TS val 312322409 ecr 0,nop,wscale 7], length 0
11:15:43.520508 vethf560a7c Out IP 172.17.0.1.40166 > 172.17.0.2.8888: Flags [S], seq 1240504208, win 32120, options [mss 1460,sackOK,TS val 312322409 ecr 0,nop,wscale 7], length 0
11:15:43.520519 vethf560a7c P   IP 172.17.0.2.8888 > 172.17.0.1.40166: Flags [R.], seq 0, ack 1240504209, win 0, length 0
11:15:43.520524 docker0 In  IP 172.17.0.2.8888 > 172.17.0.1.40166: Flags [R.], seq 0, ack 1, win 0, length 0
11:15:43.520611 docker0 Out IP 172.17.0.1.8888 > 172.17.0.2.47084: Flags [F.], seq 1, ack 1, win 249, options [nop,nop,TS val 312322409 ecr 2027316222], length 0
11:15:43.520614 vethf560a7c Out IP 172.17.0.1.8888 > 172.17.0.2.47084: Flags [F.], seq 1, ack 1, win 249, options [nop,nop,TS val 312322409 ecr 2027316222], length 0
11:15:43.521143 vethf560a7c P   IP 172.17.0.2.47084 > 172.17.0.1.8888: Flags [.], ack 2, win 251, options [nop,nop,TS val 2027316223 ecr 312322409], length 0
11:15:43.521148 docker0 In  IP 172.17.0.2.47084 > 172.17.0.1.8888: Flags [.], ack 2, win 251, options [nop,nop,TS val 2027316223 ecr 312322409], length 0
11:15:43.559266 vethf560a7c P   IP 172.17.0.2.47084 > 172.17.0.1.8888: Flags [P.], seq 1:473, ack 2, win 251, options [nop,nop,TS val 2027316261 ecr 312322409], length 472
11:15:43.559272 docker0 In  IP 172.17.0.2.47084 > 172.17.0.1.8888: Flags [P.], seq 1:473, ack 2, win 251, options [nop,nop,TS val 2027316261 ecr 312322409], length 472
11:15:43.559284 docker0 Out IP 172.17.0.1.8888 > 172.17.0.2.47084: Flags [R], seq 2759787400, win 0, length 0
11:15:43.559287 vethf560a7c Out IP 172.17.0.1.8888 > 172.17.0.2.47084: Flags [R], seq 2759787400, win 0, length 0
11:15:57.904098 eth0  In  IP 192.168.1.2.63075 > 192.168.1.3.8887: UDP, length 315
11:15:57.904098 eth0  In  IP 192.168.1.2.63075 > 172.17.0.1.8887: UDP, length 315
11:15:58.464881 docker0 Out IP 172.17.0.1.32893 > 172.17.0.2.8888: UDP, length 315
11:15:58.464885 vethf560a7c Out IP 172.17.0.1.32893 > 172.17.0.2.8888: UDP, length 315
11:16:12.932868 eth0  In  IP 192.168.1.2.63075 > 192.168.1.3.8887: UDP, length 315
11:16:12.933161 eth0  In  IP 192.168.1.2.63075 > 172.17.0.1.8887: UDP, length 315
11:16:13.456929 docker0 Out IP 172.17.0.1.48185 > 172.17.0.2.8888: UDP, length 315
11:16:13.456935 vethf560a7c Out IP 172.17.0.1.48185 > 172.17.0.2.8888: UDP, length 315

192.168.1.2 -> Client IP; 192.168.1.3 -> Docker Host IP (Linux VM)

Here is the typical command I use to run the Docker container:

docker run -it --cap-add=all --hostname debian -p 8889:8888/tcp -p 8889:8888/udp --dns-opt='options single-request' --sysctl net.ipv6.conf.all.disable_ipv6=1 --name Container1 image

However, the issue that I am facing now is that the containers are not sending any information back to the Client PC. Is there a mistake in my configuration of the Nginx or something is missing?