Docker container access to swarm IPs - docker

Question

When running docker containers a swarm cluster do the containers have access to all the IPs of the cluster nodes via ENV variables or otherwise?
I want to run an Elasticsearch instance on each node in my swarm the cluster. And they will discovery each other in unicast mode. Therefore each Elasticsearch instanc needs to be configured with the list of IPs in the cluster.

Answer 1

If you mean that container of one node can access container's IP of other node , then it is not possible . You have to use weave tool to connect container across different node or other tool .

Answer 2

If you are using latest Docker (1.13+) with a swam overlay network, you should be able to get all the cluster's node IPs through DNS round robin.(--endpoint-mode dnsrr)
1) Create an overlay network.
https://docs.docker.com/engine/swarm/networking/
docker network create \
--driver overlay \
my-network
2) Verify swam nodes:
docker#node1:~$ docker node ls
ID HOSTNAME STATUS AVAILABILITY MANAGER STATUS
5l07yt2itiee60xfq7g6c01e4 * node1 Ready Active Leader
pckn7qo3xpbxvs89ni6whyql3 node2 Ready Active
3) Create an alpine container on each nodes using "global" mode:
docker service create --mode global --endpoint-mode dnsrr --name testservice --detach=true --network my-network alpine ash -c "apk update;apk add drill; ping docker.com"
4) verify service is running:
docker#node1:~$ docker service ls
ID NAME MODE REPLICAS IMAGE PORTS
lmy5s3flw763 testservice global 2/2 alpine:latest
5) Verify that containers were deployed on individual nodes:
$ docker-machine ssh node1 "docker ps"
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
4c7055b01479 alpine:latest "ash -c 'apk updat..." 2 minutes ago Up 2 minutes testservice.5l07yt2itiee60xfq7g6c01e4.atvascigh3rvxvlzttaotkrua
$ docker-machine ssh node2 "docker ps"
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
28da546aa0d5 alpine:latest "ash -c 'apk updat..." 2 minutes ago Up 2 minutes testservice.pckn7qo3xpbxvs89ni6whyql3.ebjz4asni4w1f0srna0p3vj4a
6) Confirm individual virtual IP of each containers on node1 and node2:
| => docker-machine ssh node1 "docker exec 4c7055b01479 ash -c 'ip addr'|grep eth0"
349: eth0#if350: <BROADCAST,MULTICAST,UP,LOWER_UP,M-DOWN> mtu 1450 qdisc noqueue state UP
inet 10.0.0.2/24 scope global eth0
| => docker-machine ssh node2 "docker exec 28da546aa0d5 ash -c 'ip addr'|grep eth0"
319: eth0#if320: <BROADCAST,MULTICAST,UP,LOWER_UP,M-DOWN> mtu 1450 qdisc noqueue state UP
inet 10.0.0.3/24 scope global eth0
7) Get the container IP addresses for all containers in cluster using Drill dns tool :
| => docker-machine ssh node1 "docker exec 4c7055b01479 ash -c 'drill testservice'"
;; ->>HEADER<<- opcode: QUERY, rcode: NOERROR, id: 60920
;; flags: qr rd ra ; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;; testservice. IN A
;; ANSWER SECTION:
testservice. 600 IN A 10.0.0.3
testservice. 600 IN A 10.0.0.2
;; AUTHORITY SECTION:
;; ADDITIONAL SECTION:
;; Query time: 0 msec
;; SERVER: 127.0.0.11
;; WHEN: Thu Jul 20 19:20:49 2017
;; MSG SIZE rcvd: 83
8) Verify that containers can ping each other:
docker-machine ssh node1 "docker exec 4c7055b01479 ash -c 'ping -c2 10.0.0.3'"
PING 10.0.0.3 (10.0.0.3): 56 data bytes
64 bytes from 10.0.0.3: seq=0 ttl=64 time=0.539 ms
64 bytes from 10.0.0.3: seq=1 ttl=64 time=0.731 ms
--- 10.0.0.3 ping statistics ---
2 packets transmitted, 2 packets received, 0% packet loss
round-trip min/avg/max = 0.539/0.635/0.731 ms
docker-machine ssh node2 "docker exec 28da546aa0d5 ash -c 'ping -c2 10.0.0.2'"
PING 10.0.0.2 (10.0.0.2): 56 data bytes
64 bytes from 10.0.0.2: seq=0 ttl=64 time=0.579 ms
64 bytes from 10.0.0.2: seq=1 ttl=64 time=0.736 ms
--- 10.0.0.2 ping statistics ---
2 packets transmitted, 2 packets received, 0% packet loss
round-trip min/avg/max = 0.579/0.657/0.736 ms