We want to know what algorithm the Docker mesh uses to route requests to containers. Here's why:
We deploy our applications to self-hosted docker swarms. We use the docker routing mesh to direct traffic to the individual nodes, like this:
- internet ->
- firewall ->
- load director (nginx) ->
- nginx "least connection" routing to three swarm managers ->
- docker mesh ->
- Any of the six app containers running on three different non-manager docker nodes
Our developers suspect that the docker mesh is routing traffic round robin, which could result in some app containers being overloaded with slow requests while other containers are under-utilized. If the devs are right, we should not use the docker mesh and instead should use the load director to direct traffic to the individual containers using a smarter algorithm than round robin.
On the other hand, if the docker mesh is keeping track of how many requests are in flight to each container and delivering traffic to the container with the fewest requests, then we do not need to do the work of bypassing the docker mesh.
The question
What algorithm does the docker mesh use to direct traffic to available containers? Is it simple round robin?
Our nginx config
Our nginx receives traffic from the internet and proxies it to the docker mesh on any of the three docker manager nodes:
upstream document_service {
least_conn;
server dockermgr1.nosuchdomain:8402;
server dockermgr2.nosuchdomain:8402;
server dockermgr3.nosuchdomain:8402;
}
server {
...
proxy_pass http://document_service;
Our docker-compose config
The docker-compose file configures the service to have six replicas on the three docker runner nodes:
version: "3.4"
services:
documentsservice:
image: ${IMAGE_LOCATION}documents_service/documentsservice:prod-${COMPOSE_BUILD_TAG:-latest}
container_name: documentsservice
ports:
- "8402:80"
...
deploy:
replicas: 6
placement:
constraints: [node.role != manager]
resources:
limits:
memory: 1024MB
update_config:
parallelism: 1
order: start-first
failure_action: continue
Versions
- docker-ce 5:19.03.12~3-0~debian-buster
- nginx-full 1.14.2-2+deb10u4
- docker-compose: 1.27.4
