Sometimes you need to export multiple instances of the same service with a specific IP using same port outside of a docker swarm environment.
Using docker swarm environment is easy to have several instances of the same service exporting some API on the same port. The swarm will take care of load balancing the services and ports will not clash. But what if we need to have several instances of the same service (running as a container) that we want to load balance from outside a docker swarm.
The solution is to use virtual IPs and map the service ports not to the local host but to the virtual IPs.
STEP 1: Define virtual interfaces under Linux
With the following we define 3 virtual interfaces.
ip link add virtual0 link enp2s0 type macvlan mode bridge ip link add virtual1 link enp2s0 type macvlan mode bridge ip link add virtual2 link enp2s0 type macvlan mode bridge
STEP 2: Add the virtual IPs
With the following we add 3 virtual IPs to the defined virtual interfaces.
ip address add 220.127.116.11/24 broadcast 18.104.22.168 dev virtual0 ip address add 22.214.171.124/24 broadcast 126.96.36.199 dev virtual1 ip address add 188.8.131.52/24 broadcast 184.108.40.206 dev virtual2
STEP 3: Bring them up
With the following we bring up the IPs
ip link set virtual0 up ip link set virtual1 up ip link set virtual2 up
STEP 4: Define services using the virtual IPs
The following is an example of how to define 3 jetty based services in a docker-compose that use the virtual IPs.
node1: image: jetty volumes: - /home/docker-volumes/node1:/opt/jetty.base/node:Z env_file: - ./node.env ports: - "220.127.116.11:8080:8080" - "18.104.22.168:8443:8443" - "22.214.171.124:9101:9101" working_dir: /opt/jetty.base/node/ command: ["./start.sh"] node2: image: jetty volumes: - /home/docker-volumes/node2:/opt/jetty.base/node:Z env_file: - ./node.env ports: - "126.96.36.199:8080:8080" - "188.8.131.52:8443:8443" - "184.108.40.206:9101:9101" working_dir: /opt/jetty.base/node/ command: ["./start.sh"] node3: image: jetty volumes: - /home/docker-volumes/node3:/opt/jetty.base/node:Z env_file: - ./node.env ports: - "220.127.116.11:8080:8080" - "18.104.22.168:8443:8443" - "22.214.171.124:9101:9101" working_dir: /opt/jetty.base/node/ command: ["./start.sh"]
With the above definition I can have now three instances of the same jetty based service exporting an API on the 8080 (http) and 8443 (https) ports but having different IPs.
A load balancing can be done now on this IPs outside a swarm.
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