moby--moby/libnetwork/cmd/ssd

Docker Swarm Service Driller(ssd)

ssd is a troubleshooting utility for Docker swarm networks.

control-plane and datapath consistency check on a node

ssd checks for the consistency between docker network control-plane (from the docker daemon in-memory state) and kernel data path programming. Currently the tool checks only for the consistency of the Load balancer (implemented using IPVS).

In a three node swarm cluser ssd status for a overlay network ov2 which has three services running, each replicated to 3 instances.

vagrant@net-1:~/code/go/src/github.com/docker/docker-e2e/tests$ docker run -v /var/run/docker.sock:/var/run/docker.sock -v /var/run/docker/netns:/var/run/docker/netns --privileged --net=host sanimej/ssd ov2
Verifying LB programming for containers on network ov2
Verifying container /s2.3.ltrdwef0iqf90rqauw3ehcs56...
service s2... OK
service s3... OK
service s1... OK
Verifying container /s3.3.nyhwvdvnocb4wftyhb8dr4fj8...
service s2... OK
service s3... OK
service s1... OK
Verifying container /s1.3.wwx5tuxhnvoz5vrb8ohphby0r...
service s2... OK
service s3... OK
service s1... OK
Verifying LB programming for containers on network ingress
Verifying container Ingress...
service web... OK

ssd checks the required iptables programming to direct an incoming packet with the : to the right :

control-plane consistency check across nodes in a cluster

Docker networking uses a gossip protocol to synchronize networking state across nodes in a cluster. ssd's gossip-consistency command verifies if the state maintained by all the nodes are consistent.

In a three node cluster with services running on an overlay network ov2 ssd consistency-checker shows 

vagrant@net-1:~/code/go/src/github.com/docker/docker-e2e/tests$ docker run -v /var/run/docker.sock:/var/run/docker.sock -v /var/run/docker/netns:/var/run/docker/netns --privileged sanimej/ssd ov2 gossip-consistency
Node id: sjfp0ca8f43rvnab6v7f21gq0 gossip hash c57d89094dbb574a37930393278dc282

Node id: bg228r3q9095grj4wxkqs80oe gossip hash c57d89094dbb574a37930393278dc282

Node id: 6jylcraipcv2pxdricqe77j5q gossip hash c57d89094dbb574a37930393278dc282

This is hash digest of the control-plane state for the network ov2 from all the cluster nodes. If the values have a mismatch docker network inspect --verbose on the individual nodes can help in identifying what the specific difference is.