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Docker-compose example

  • Consul cluster: 3 nodes
  • Example app: 3 replicas, each replica connect to different consul node in cluster
  • Nginx + consul-template node. It is used as gateway & loadbalancer

Notes

A. Each example instance needs consul address, which provided as a ENV variable.

  backend2:
    build: ../example
    image: zhenik/akka-http-example
    environment:
    - DISCOVERY_HOST=consul1
    - APPLICATION_HOST=backend2

B. Nginx + consul-template requires 2 volumes.

  nginx:
    build: ../
    image: seges/nginx-consul
    ports:
    - "80:80"
    - "8080:8080"
    - "443:443"
    volumes:
    #      templates
    - "./nginx-setup/templates/template.ctmpl:/etc/consul-template/templates/template.ctmpl"
    #      config
    - "./nginx-setup/conf:/etc/consul-template/conf"
    depends_on:
      - consul1
  • Volume with templates. Templates contains instruction how to render target files.
upstream app-example {
  least_conn;
    {{range service "example-app"}}server {{.Address}}:{{.Port}} max_fails=3 fail_timeout=60 weight=1;
  {{else}}server 127.0.0.1:65535; # force a 502{{end}}
}
server {
  listen 8080;
  server_name localhost;

  location / {
    proxy_pass http://app-example;
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header Host $host;
    proxy_set_header X-Real-IP $remote_addr;
  }
}
  • Volume with config for consul-template

All config can be found in consul-template documentation

consul{
  address = "consul1:8500" // which consul connect to 
}

template {
    source = "/etc/consul-template/templates/template.ctmpl"  // source file for tmpl
    destination = "/etc/nginx/conf.d/default.conf"            // target file with rendered data
    command = "/etc/init.d/nginx reload"                     
    command_timeout = "60s"
}

If you want extend solution

Problems

Problem A: What if consul1 is down, but cluster is resilient and consul2 consul3 are accessible.

Problem B: Volumes with templates, point explicitly to specific file. How to add more templates.

Problem C: Gateway is bottleneck. It is only one node.

Possible solutions

Problem A1: Bootstrap consul cluster.

Problem A2: Setup consul-agent on seges/nginx-consul image. Solution from documentation

address = "127.0.0.1:8500"

This is the address of the Consul agent. By default, this is 127.0.0.1:8500, which is the default bind and port for a local Consul agent. It is not recommended that you communicate directly with a Consul server, and instead communicate with the local Consul agent. There are many reasons for this, most importantly the Consul agent is able to multiplex connections to the Consul server and reduce the number of open HTTP connections. Additionally, it provides a "well-known" IP address for which clients can connect.

Problem B1: Use directories for consul-template config and render multiple templates.

Problem C1 draft: Create cluster of gateways. Redirect if not accessible.