Passing "CASSANDRA_RACK" and "CASSANDRA_DC" do nothing

[antimack]

Hi.
I've started up 3 nodes Cassandra 2.1.13 cluster with passing some env variables like:
CASSANDRA_CLUSTER_NAME=mycluster
CASSANDRA_DC=dc2
CASSANDRA_RACK=rack2

but when I'm using "nodetool status" on a first node(seed node in my case) I see default "datacenter1" and "rack1" so it seems that passing this variables don't do nothing

root@39559689ed20:/# cat /etc/cassandra/cassandra-rackdc.properties | egrep -v "^\s*(#|$)"
dc= dc2
rack= rack2

root@39559689ed20:/# nodetool status
Datacenter: datacenter1
=======================
Status=Up/Down
|/ State=Normal/Leaving/Joining/Moving
--  Address      Load       Tokens  Owns (effective)  Host ID                               Rack
UN  192.168.0.4  107.39 KB  256     69.0%             6c39fcc4-a54d-407a-811f-f4bc3d5587b7  rack1
UN  192.168.0.3  120.16 KB  256     67.2%             f04417e4-0124-4eb4-842a-37636a14ab0d  rack1
UN  192.168.0.2  112.63 KB  256     63.8%             65ad3bdb-519e-4568-8370-8f53d0a0fd49  rack1

[muehan]

same here. created container
docker run --name=n1 -d cassandra -CASSANDRA_DC=DC1 -CASSANDRA_RACK=RAC1
but status says

*******:~ # docker exec -it n1 nodetool status
Datacenter: datacenter1
=======================
Status=Up/Down
|/ State=Normal/Leaving/Joining/Moving
--  Address     Load       Tokens       Owns    Host ID                               Rack
UN  172.18.0.2  97.61 KB   256          ?       f7ee318d-2c00-44f1-9172-811962f8987e  rack1

Note: Non-system keyspaces don't have the same replication settings, effective ownership information is meaningless

[yosifkit]

We've had this since #6. Dang 😢. Is there something we need to do to get cassandra to use the cassandra-rackdc.properties?

[tianon]

I think the discussion in #39 (comment) is relevant here, since it looks like setting endpoint_snitch requires additional configuration depending on which snitch you choose, so I'm more +1 to reverting this functionality and adding more documentation. (since we'll need more documentation as-is already, since you have to set the endpoint_snitch as well)

[yosifkit]

You do need to set the snitch. This works to get the file used:

$ docker run -d \
    -e CASSANDRA_CLUSTER_NAME=mycluster \
    -e CASSANDRA_DC=dc2 \
    -e CASSANDRA_RACK=rack2 \
    -e CASSANDRA_ENDPOINT_SNITCH=GossipingPropertyFileSnitch \
    --name cass cassandra

Not sure about reverting 😕, but I am leaning -1 on it. I don't like removing functionality.

As for the other snitches needing more config values, it doesn't seem like we do:

• SimpleSnitch, default value, just works
• RackInferringSnitch, uses ip to determine rack and dc, probably not used in practice
  • "Use this snitch as an example of writing a custom Snitch class." -from the docs
• PropertyFileSnitch needs a complete network map of your cassandra servers, which requires a whole file that would need to be added to the image (custom, not something we could conceivably generate)
• GossipingPropertyFileSnitch, the one that uses our CASSANDRA_DC and CASSANDRA_RACK generated file
• Ec2Snitch, uses amazon private ips, may work with --net=host or possibly -e CASSANDRA_BROADCAST_ADDRESS="private aws ip" -p ...
• EC2MultiRegionSnitch, uses public and private amazon ip address, so BROADCAST_ADDRESS and friends should work
  • will probably only work with --net=host since it needs access to the public and private IP of the host

(This is just from reading the documentation, I have not tested these.)

[j-potts]

@yosifkit what doc did you pull that from? I ran into this same issue, but found that SimpleSnitch does not "recognize" dc or rack info per the Datastax Cassandra doc: https://docs.datastax.com/en/cassandra/2.1/cassandra/architecture/architectureSnitchSimple_c.html

I tested this using docker-compose with CASSANDRA_ENDPOINT_SNITCH: "SimpleSnitch" set, it did not add my Cassandra nodes to the datacenter specified with CASSANDRA_DC. However, if I change the endpoint snitch to CASSANDRA_ENDPOINT_SNITCH: "GossipingPropertyFileSnitch" it works.

If anything, it seems like updating the Docker hub doc for CASSANDRA_DC to mention that the default SimpleSnitch will not honor this setting and pointing to the relevant Datastax doc would be worth the effort.

[markglh]

This seems like correct behaviour to me, it's just a change to the documentation that's required to make it clear how Cassandra works under these circumstances.

[j-potts]

@markglh 👍