Routing Mesh (Global Traffic Router)

• Routes ingress (incoming) packets for a Service to proper Task
• Spans all nodes in Swarm
• Uses IPVS from Linux Kernel
• Load balances Swarm Services across their Tasks

• Two ways this works:

  • Container-to-container in an Overlay network (uses VIP)
  • External traffic incoming to published ports (all nodes listen)

• This is stateless load balancing

• This LB is at OSI Layer 3 (TCP), not Layer 4 (DNS)
• Both limitation can be overcome with:
  • Nginx or HAProxy LB proxy, or:
  • Docker Enterprise Edition, which comes with built-in L4 web proxy

• Similar to hardware load balancer

Example

• Let's run `elasticsearch service

[node1] ~> docker service create --name search --replicas 3 -p 9200:9200 elasticsearch:2
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[node1] ~> docker service ps search
ID                  NAME                IMAGE               NODE                DESIRED STATE       CURRENT STATE           ERROR               PORTS
p1jg45oq9tfi        search.1            elasticsearch:2     node3               Running             Running 7 seconds ago
jsw9g0vh6xkz        search.2            elasticsearch:2     node1               Running             Running 7 seconds ago
ni2c3sagawbh        search.3            elasticsearch:2     node2               Running             Running 7 seconds ago

• The load is distributed to tasks

External links

• Use swarm mode routing mesh