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# 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 cluster ssd status for a overlay network `ov2` which has three services running, each replicated to 3 instances.
````bash
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 <host ip>:<published port> to the right <backend ip>:<target port>
### 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.
````bash
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.
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