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From Eunsu Kim <>
Subject Re: Default Single DataCenter -> Multi DataCenter
Date Tue, 11 Sep 2018 05:25:58 GMT

Thank you for your responses.

I’ll share my adding datacenter plan. If you see problems, please respond.

The sentence may be a little awkward because I am so poor at English that I am being helped
by a translator.

I've been most frequently referred to.( <>)
Thank you for your cleanliness. (Pradeep Chhetri)

I will also upgrade the version as Alain Rodriguez's advice.


Step 1. Stop all existing clusters. (My service is paused.)

Step 2. Install Cassandra 3.11.3 and copy existing conf files.

Step 3. Modify for existing nodes. dc=mydc1 rack=myrack1
     Q. I think this modification will not affect the existing data because it was SimpleSnitch
before, right?

Step 4. In the caseandra.yaml of existing nodes, endpoint_snitch is changed to GossippingPropertyFileSnitch.

Step 5. Restart the Cassandra of the existing nodes. (My service is resumed.)

Step 6. Change the settings of all existing clients to DCAwareRobinPolicy and refer to mydc1.
Consistency level is LOCAL_ONE. And rolling restart.
      Q. Isn't it a problem that at this point, DCAwareRobinPolicy and RoundRobinPolicy coexist?

Step 7. Alter my keyspace and system keyspace(system_distributed, system_traces) :  SimpleStrategy(RF=2)
-> { 'class' : 'NetworkTopologyStrategy', ‘mydc1’ : 2 }

Step 8. Install Cassandra in a new cluster, copying existing conf files, and setting it to dc=mydc2 rack=myrack2

Step 9. Adding a new seed node to the cassandra.yaml of the existing cluster (mydc1) and restart.
      Q1. Must I add the new seed nodes in five all existing nodes?
      Q2. Don't I need to update the seed node settings of the new cluster (mydc2)?

Step 10. Alter my keyspace and system keyspace(system_distributed, system_traces) :  { 'class'
: 'NetworkTopologyStrategy', ‘mydc1’ : 1, ‘mydc2’ : 1 }

Step 11. Run 'nodetool rebuild — mydc1’ in turn, in the new node.


I'll run the procedure on the development envrionment and share it.

Thank you.

> On 10 Sep 2018, at 10:26 PM, Pradeep Chhetri <> wrote:
> Hello Eunsu, 
> I am going through the same exercise at my job. I was making notes as i was testing the
steps in my preproduction environment. Although I haven't tested end to end but hopefully
this might help you: <>
> Regards,
> Pradeep
> On Mon, Sep 10, 2018 at 5:59 PM, Alain RODRIGUEZ < <>>
> Adding a data center for the first time is a bit tricky when you haven't been considering
it from the start.
> I operate 5 nodes cluster (3.11.0) in a single data center with SimpleSnitch, SimpleStrategy
and all client policy RoundRobin.
> You will need:
> - To change clients, make them 'DCAware'. This depends on the client, but you should
be able to find this in your Cassandra driver (client side).
> - To change clients, make them use 'LOCAL_<WHATEVER>' consistency ('LOCAL_ONE'/'LOCAL_QUORUM'
being the most common).
> - To change 'SimpleSnitch' for 'EC2Snitch' or 'GossipingPropertyFileSnitch' for example,
depending on your context/preference
> - To change 'SimpleStrategy' for 'NetworkTopologyStrategy' for all the keyspaces, with
the desired RF. I take the chance to say that switching to 1 replica only is often a mistake,
you can indeed have data loss (which you accept) but also service going down, anytime you
restart a node or that a node goes down. If you are ok with RF=1, RDBMS might be a better
choice. It's an anti-pattern of some kind to run Cassandra with RF=1. Yet up to you, this
is not our topic :). In the same kind of off-topic recommendations, I would not stick with
C*3.11.0, but go to C*3.11.3 (if you do not perform slice delete, there is still a bug with
this apparently)
> So this all needs to be done before starting adding the new data center. Changing the
snitch is tricky, make sure that the new snitch uses the racks and dc names currently in use
in your cluster for the current cluster, if not the data could not be accessible after the
configuration change.
> Then the procedure to add a data center is probably described around. I know I did this
detailed description in 2014, here it is:
but you might find better/more recent documentation than this one for this relatively common
process, like the documentation you linked.
> If you are not confident or have doubts, you can share more about the context and post
your exact plan, as I did years ago in the mail previously linked. People here should be able
to confirm the process is ok before you move forward, giving you an extra confidence.
> C*heers,
> -----------------------
> Alain Rodriguez - @arodream - <>
> France / Spain
> The Last Pickle - Apache Cassandra Consulting
> <>
> Le lun. 10 sept. 2018 à 11:05, Eunsu Kim < <>>
a écrit :
> Hello everyone
> I operate 5 nodes cluster (3.11.0) in a single data center with SimpleSnitch, SimpleStrategy
and all client policy RoundRobin.
> At this point, I am going to create clusters of the same size in different data centers.
> I think these two documents are appropriate, but there is confusion because they are
referenced to each other.
> Anyone who can clearly guide the order? Currently RF is 2 and I want to have only one
replica in the NetworkTopologyStrategy.
> A little data loss is okay.
> Thank you in advanced..

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