Cassandra Nodes not linking in Docker - docker

Question

I am watching a kind of old video on PluralSight for Cassandra and linking works with the method below. However, it is not working with the current docker version. This is how I am linking different nodes. For example:
docker run --name=n1 -d tobert/cassandra
docker run --name n2 -d tobert/cassandra -seeds 172.17.0.7
172.17.0.7 is the IP address when I run the command
docker inspect -f '{{ .NetworkSettings.IPAddress}}' n1
However, only one node is allowed to run at a time is seems. When I run the command
docker ps
or
docker exec -it n1 nodetool status
only one of the containers are running. When I try to inspect a container's ip address, it returns empty. Is there another way to link cassandra nodes in docker?

Answer 1

Manage to resolve this.
It appears to have been an issue with the docker machine created by the "Docker quickstart terminal". Perhaps related to default memory of 1024?
Recreating the machine solved it for me
docker-machine rm default
docker-machine create -d virtualbox --virtualbox-memory=4096 default

Answer 2

Yes, Dashu is right, you need more than the default memory to run multiple Cassandra instances. See similar Twitter thread here: https://twitter.com/perksc/status/641159044225466368.
The -seeds parameter is specific to the entrypoint of this Cassandra docker container and facilitates Cassandra's own clustering (see Github project here: https://github.com/tobert/cassandra-docker). With this feature you don't need to use Docker's own container linking to establish a cluster.
(I'm the author of the Pluralsight course in question. Funny that the course is less than a year old, but so much has changed in Docker since then!)

Answer 3

I was having the same problem. It is solved with using the memory parameter -m 4g. So I initialize the nodes with 4 g.
A - Changing The Docker Memory
And it is good to increase the Docker Memory;
B - My Setup
Windows Version: Windows 10 Pro
Memory: 16 gb
Docker version;
docker --version
Docker version 18.09.2, build 6247962
C - Solution Demo
Initializing 1st cassandra node;
docker run --name=n1 -d -m 4g tobert/cassandra
Getting the ip of the first node;
docker inspect -f "{{ .NetworkSettings.IPAddress }}" n1
The output of the above command is;
172.17.0.3
Initializing the second Cassandra node linking with the first one;
docker run --name n2 -d -m 4g tobert/cassandra -seeds 172.17.0.3
Running the nodetools status command at first node;
docker exec -it n1 nodetool status
Datacenter: datacenter1
=======================
Status=Up/Down
|/ State=Normal/Leaving/Joining/Moving
-- Address Load Tokens Owns (effective) Host ID Rack
UN 172.17.0.3 51.5 KB 256 100.0% 002150d0-90b9-4f8f-861f-0d0205e3ea72 rack1
UN 172.17.0.4 82.46 KB 256 100.0% 05c06381-778e-4989-860b-756d05c8cfbc rack1
Running the nodetools status command at second node;
docker exec -it n2 nodetool status
Datacenter: datacenter1
=======================
Status=Up/Down
|/ State=Normal/Leaving/Joining/Moving
-- Address Load Tokens Owns (effective) Host ID Rack
UN 172.17.0.3 51.5 KB 256 100.0% 002150d0-90b9-4f8f-861f-0d0205e3ea72 rack1
UN 172.17.0.4 82.46 KB 256 100.0% 05c06381-778e-4989-860b-756d05c8cfbc rack1

Answer 4

You can link docker containers with --link flag:
docker run --name n1 tobert/cassandra
docker run --name n2 --link n1:cassandra tobert/cassandra -seeds cassandra
Communication across links, from docker documentation, contains detailed explanation how to use --link flag.
I also run your commands and it works on my machine.
Below is output of the command: docker exec -it n1 nodetool status:
Datacenter: datacenter1
=======================
Status=Up/Down
|/ State=Normal/Leaving/Joining/Moving
-- Address Load Tokens Owns (effective) Host ID Rack
UN 172.17.0.3 72 KB 256 100.0% f0a34a45-5f7a-46ff-8fe6-1cf5ff36a3e3 rack1
UN 172.17.0.2 51.46 KB 256 100.0% 8036177e-515c-42b1-9263-3b815c25bde6 rack1
Also, when -seed parameter is wrong (not existing ip address) second container is waiting for a while and after ~30s terminates with exeception:
ERROR [main] 2016-02-07 19:12:11,081 CassandraDaemon.java:541 - Exception encountered during startup
java.lang.RuntimeException: Unable to gossip with any seeds
at org.apache.cassandra.gms.Gossiper.doShadowRound(Gossiper.java:1307) ~[apache-cassandra-2.1.7.jar:2.1.7]
at org.apache.cassandra.service.StorageService.checkForEndpointCollision(StorageService.java:533) ~[apache-cassandra-2.1.7.jar:2.1.7]
So I think n2 is not able to access n1 - please double check your n1 ip address (to check your n2 logs run: docker exec xxxx tail -f /data/log/system.log -n 100, where xxxx - n2 container id).
If you do not have any specific requirements on Cassandra version you can also check image from official repository: https://hub.docker.com/_/cassandra/.