Since my Cassandra cluster is replicated across three availability zones, I would like to backup only one availability zone to lower the backup costs. I have also experimented restoring nodes in a single availability zone and got back most of my data in a test environment. I would like to know if there are any drawbacks to this approach before deploying this solution in production. Is anyone following this approach in your production clusters?
Note: As I backup at regular intervals, I know that I may loose updates happened to other two AZ nodes quorum at the time of snapshot but that's not a problem.
You can backup only specific dc, or even nodes.
AFAIK, the only drawback is does your data consistent/up-to-date, and since you can afford to lose some data it shouldn't be a problem. And if you, for example performing writes with ALL consistency level, the data should be up-to-date on all nodes.
BUT, you must be sure that your data is indeed replicated between multi a-z, by playing with rack/dc properties or using ec2 switch that supports multi a-z.
EDIT:
Global Snapshot
Running nodetool snapshot is only run on a single node at a time.
This only creates a partial backup of your entire data. You will want
to run nodetool snapshot on all of the nodes in your cluster. But
it’s best to run them at the exact same time, so that you don’t have
fragmented data from a time perspective. You can do this a couple of
different ways. The first, is to use a parallel ssh program to
execute the nodetool snapshot command at the same time. The second,
is to create a cron job on each of the nodes to run at the same time.
The second assumes that your nodes have clocks that are in sync, which
Cassandra relies on as well.
Link to the page:
http://datascale.io/backing-up-cassandra-data/
Related
I have a mixed workload cluster across multiple datacenters. I have ran the sstableloader command for the tables I want to restore using snapshots which I had backed up. I have added commit log files which I had backed up from archive to a restore directory on all nodes. I have updated the commitlog_archiving.properties file with these configs.
What is the correct way and order to restart nodes of my cluster?
Do these considerations apply for restarting as well?
As a general rule, we recommend restarting seed nodes in the DC first before other nodes so gossip propagation happens faster particularly for larger clusters (arbitrarily 15+ nodes). It is important to note that a restart is not required if you restored data using sstableloader.
If you are just performing a rolling restart then the order of the DCs does not matter. But it matters if you are starting up a cluster from a cold shutdown meaning all nodes are down and the cluster is completely offline.
When starting from a cold shutdown, it is important to start with the "Analytics DC" (nodes running in Analytics mode, i.e with Spark enabled) because it makes it easier to elect a Spark master. Assuming that the replication for Analytics keyspaces are configured with the recommended replication factor of 3, you will need to start 2 or 3 nodes beginning with the seeds ideally 1 minute apart because the LeaderManager requires a quorum of nodes to elect a Spark master.
We recommend leaving DCs with nodes running in Search mode (with Solr enabled) last as a matter of convenience so that all the other DCs are operational before the cluster starts accepting Search requests from the application(s). Cheers!
If you've done all of that, I don't think the order matters too much. Although, you should restart your seed nodes first, that way the nodes in the cluster have a common cluster entrypoint to find their way back in and correctly rejoin.
We have set up a backup/restore procedure for our Cassandra production environment via snapshots. The snapshot files, schema and token ring information are copied to S3.
The production cluster is a 3-node-cluster with a replication factor of 3.
For development and test, I would like to restore the snapshots from production into separated clusters. To save money and to keep maintenance easy, it would be nice to restore only the snapshot from one production node. Since we are using a replication factor of 3 in a 3-node-cluster, each snapshot should have all rows. Consistency is also not important for our use-case.
Is it possible (and how) to restore only a single snapshot?
All of your data should exist on all 3 nodes so copying the sstables from any 1 node to your test cluster should be sufficient. Making sure theres a recent repair beforehand may be good idea if worried about consistency.
First create the same schema on the test cluster. Then you can simply take a snapshot with nodetool snapshot -t cloneme. Once complete, copy all the sstables from the folder that is created (cloneme) into the equivalent tables folder on your test cluster. Then run nodetool refresh.
It gets much more complicated if you have a different topology (more nodes, different RF) but since your going with "every node has all the data" its pretty trivial.
Worth mentioning that OpsCenter has a feature to automate the copying of a backup to other clusters.
I have read about Cassandra backup & recovery here, and have a few questions:
Do the native Cassandra CLI commands suffice? I see a lot of people writing scripts and custom-making their own solutions.
What other tools out there would you recommend for Cassandra backup and recovery? I am looking for something that can help me manage the backup images (e.g. with point-in-time)
Do I need to invest significantly more into storage if I opt to backup my Cassandra tables?
Any insights would be appreciated.
Please try to limit your questions to one actual question.
Do the native Cassandra CLI commands suffice?
I assume that you mean nodetool snapshot, so for the most-part, "yes." In addition, many users choose to also enable incremental backups. With a combination of using snapshots and incremental backups (from the linked doc) "provides a dependable, up-to-date backup mechanism."
I see a lot of people writing scripts and custom-making their own solutions.
I have a backup script that runs on my nodes nightly. There are two reasons for this.
I don't want to have to manually take a snapshot for each keyspace every week, so I have the script do it.
Snapshot and incremental backup files don't remove themselves, so I have the script do that after a certain time threshold.
What other tools out there would you recommend for Cassandra backup and recovery?
DataStax OpsCenter allows you to schedule backups, but I believe that is only a valid option in the Enterprise edition. You could also look at Netflix's Cassandra backup/recovery tool called Priam. There's also a company called Talena which claims to provide an extensive enterprise-grade backup solution for Cassandra (I don't know anyone who uses them, but they hit me with a marketing email recently so I thought I'd mention it).
Do I need to invest significantly more into storage if I opt to backup my Cassandra tables?
Incremental backups and snapshots can take up a great deal of space if you don't stay on top of them (deleting and/or archiving them). I would try them both out, and keep an eye on your disk usage while you do. If your business requirements have a statement on terms of service (how far back you would need to be able to restore to), you should be able to figure out how many days-worth of backups it makes sense for you to keep around. That should tell you whether or not you need more disk to fulfill those obligations.
Edit 20181205
Do you run nodetool snapshot on each node? What would be the approach if there are three nodes with 100% replication.
Typically yes, nodetool snapshot needs to be run on each node. This helps to ensure backup coverage, as not all of the nodes may be responsible for all of the data.
However, if your cluster runs in a configuration where number of nodes equals your RF, then each node has a complete copy of the data. In that case, you would need to run nodetool snapshot on only one node; as long as you are confident that repairs are running regularly and your data is consistent.
With regards to point-in-time backup and recovery of Cassandra, there are a few aspects that you need to consider depending on what your needs and limitations are:
Storage Footprint
All the solutions available today will put a big strain on your infrastructure as they would require you to store 3x the data that you absolutely need to, assuming you have a replication factor of 3.
I agree with #Aaron, you need to manage the snapshots yourself because the tools will not do “garbage collection” for you :)
Failure resiliency
All the solutions out there, opscenter and others, provide limited failure resiliency. You will lose data if a Cassandra node goes down during a backup window.
This situation is exasperated when you have incremental backups and node failure happens during an incremental
Recovery time/speed
Note that you may have to go through a “repair” process during recovery. This is needed because the node level snapshots that the native tools provide are not consistent across the cluster.
Depending on your RTO/RPO needs, this may not be adequate. I suggest you test both the backup and recovery times for your operations before you arrive at any solution.
If you are looking for enterprise grade solution for backup and recovery of Cassandra, you may want to check out the solution offered by “Datos IO”. It reduces your storage footprint by 3x while also providing failure resiliency and cluster consistency.
We are considering additional backup strategies for our Cassandra database.
Currently we use:
nodetool snapshot - allows us to take a snapshot of all data on a given node at any time
replication level in itself is a backup - if any node ever goes down we still have additional copies of the data
Is there any other efficient strategy? The biggest issue is that we need a copy of life data in additional datacenter, which has just one server. So, for example let's say we 3 Cassandra servers, that we want to replicate to one backup Cassandra server in a second datacenter. the only way I can think we can do it is to set the replication level to 4. That means all the data will have to be written to all servers at all times.
We are also considering running Cassandra on top of some network distributed system like HDFS. Correct me if I'm wrong but that would be a very inefficient use of Cassandra?
Are there any other efficient backup strategies for Cassandra that can backup the current data without impairing it's performance?
So there is a fair amount of documentation on how to scale up a Cassandra, but is there a good resource on how to "unscale" Cassandra and remove nodes from the cluster? Is it as simple as turning off a node, letting the cluster sync up again, and repeating?
The reason is for a site that expects high spikes of traffic, climbing from the daily few thousand hits to hundreds of thousands over a few days. The site will be "ramped up" before hand, starting up multiple instances of the web server, Cassandra, etc. After the torrent of requests subsides, the goal is to turn off the instances that are not longer used, rather than pay for servers that are just sitting around.
If you just shut the nodes down and rebalance cluster, you risk losing some data, that exist only on removed nodes and hasn't replicated yet.
Safe cluster shrink can be easily done with nodetool. At first, run:
nodetool drain
... on the node removed, to stop accepting writes and flush memtables, then:
nodetool decommission
To move node's data to other nodes, and then shut the node down, and run on some other node:
nodetool removetoken
... to remove the node from the cluster completely. The detailed documentation might be found here: http://wiki.apache.org/cassandra/NodeTool
From my experience, I'd recommend to remove nodes one-by-one, not in batches. It takes more time, but much more safe in case of network outages or hardware failures.
When you remove nodes you may have to re-balance the cluster, moving some nodes to a new token. In a planed downscale, you need to:
1 - minimize the number of moves.
2 - if you have to move a node, minimize the amount of transfered data.
There's an article about cluster balancing that may be helpful:
Balancing Your Cassandra Cluster
Also, the begining of this video is about add node and remove node operations and best strategies to minimize the cluster impact in each of these operations.
Hopefully, these 2 references will give you enough information to plan your downscale.
First, on the node, which will be removed, flush memory (memtable) to SSTables on disk:
-nodetool flush
Second, run command to leave a cluster:
-nodetool decommission
This command will assign ranges that the node was responsible for to other nodes and replicates the data appropriately.
To monitor a process you can use command:
- nodetool netstats
Found an article on how to remove nodes from Cassandra. It was helpful for me scaling down cassandra.All actions are described step-by-step there.