CockroachDB's flexible replication controls make it trivially easy to run a single CockroachDB cluster across cloud platforms and to migrate data from one cloud to another without any service interruption. This page walks you through a local simulation of the process.

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Step 1. Install prerequisites

In this tutorial, you'll use CockroachDB, the HAProxy load balancer, and CockroachDB's version of the YCSB load generator, which requires Go. Before you begin, make sure these applications are installed:

  • Install the latest version of CockroachDB.
  • Install HAProxy. If you're on a Mac and using Homebrew, use brew install haproxy.
  • Install Go version 1.9 or higher. If you're on a Mac and using Homebrew, use brew install go. You can check your local version by running go version.
  • Install the CockroachDB version of YCSB: go get github.com/cockroachdb/loadgen/ycsb

Also, to keep track of the data files and logs for your cluster, you may want to create a new directory (e.g., mkdir cloud-migration) and start all your nodes in that directory.

Step 2. Start a 3-node cluster on "cloud 1"

If you've already started a local cluster, the commands for starting nodes should be familiar to you. The new flag to note is --locality, which accepts key-value pairs that describe the topography of a node. In this case, you're using the flag to specify that the first 3 nodes are running on cloud 1.

In a new terminal, start node 1 on cloud 1:

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$ cockroach start \
--insecure \
--locality=cloud=1 \
--store=cloud1node1 \
--host=localhost \
--cache=100MB \
--join=localhost:26257,localhost:26258,localhost:26259

In a new terminal, start node 2 on cloud 1:

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$ cockroach start \
--insecure \
--locality=cloud=1 \
--store=cloud1node2 \
--host=localhost \
--port=25258 \
--http-port=8081 \
--cache=100MB \
--join=localhost:26257,localhost:26258,localhost:26259

In a new terminal, start node 3 on cloud 1:

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$ cockroach start \
--insecure \
--locality=cloud=1 \
--store=cloud1node3 \
--host=localhost \
--port=25259 \
--http-port=8082 \
--cache=100MB \
--join=localhost:26257,localhost:26258,localhost:26259

Step 3. Initialize the cluster

In a new terminal, use the cockroach init command to perform a one-time initialization of the cluster:

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$ cockroach init \
--insecure \
--host=localhost \
--port=26257

Step 4. Set up HAProxy load balancing

You're now running 3 nodes in a simulated cloud. Each of these nodes is an equally suitable SQL gateway to your cluster, but to ensure an even balancing of client requests across these nodes, you can use a TCP load balancer. Let's use the open-source HAProxy load balancer that you installed earlier.

In a new terminal, run the cockroach gen haproxy command, specifying the port of any node:

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$ cockroach gen haproxy \
--insecure \
--host=localhost \
--port=26257

This command generates an haproxy.cfg file automatically configured to work with the 3 nodes of your running cluster. In the file, change bind :26257 to bind :26000. This changes the port on which HAProxy accepts requests to a port that is not already in use by a node and that won't be used by the nodes you'll add later.

global
  maxconn 4096

defaults
    mode                tcp
    timeout connect     10s
    timeout client      1m
    timeout server      1m

listen psql
    bind :26000
    mode tcp
    balance roundrobin
    server cockroach1 localhost:26257
    server cockroach2 localhost:26258
    server cockroach3 localhost:26259

Start HAProxy, with the -f flag pointing to the haproxy.cfg file:

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$ haproxy -f haproxy.cfg

Step 5. Start a load generator

Now that you have a load balancer running in front of your cluster, let's use the YCSB load generator that you installed earlier to simulate multiple client connections, each performing mixed read/write workloads.

In a new terminal, start ycsb, pointing it at HAProxy's port:

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$ $HOME/go/bin/ycsb -duration 20m -tolerate-errors -concurrency 10 -max-rate 1000 'postgresql://root@localhost:26000?sslmode=disable'

This command initiates 10 concurrent client workloads for 20 minutes, but limits the total load to 1000 operations per second (since you're running everything on a single machine).

Step 6. Watch data balance across all 3 nodes

Now open the Admin UI at http://localhost:8080 and hover over the SQL Queries graph at the top. After a minute or so, you'll see that the load generator is executing approximately 95% reads and 5% writes across all nodes:

CockroachDB Admin UI

Scroll down a bit and hover over the Replicas per Node graph. Because CockroachDB replicates each piece of data 3 times by default, the replica count on each of your 3 nodes should be identical:

CockroachDB Admin UI

Step 7. Add 3 nodes on "cloud 2"

At this point, you're running three nodes on cloud 1. But what if you'd like to start experimenting with resources provided by another cloud vendor? Let's try that by adding three more nodes to a new cloud platform. Again, the flag to note is --locality, which you're using to specify that these next 3 nodes are running on cloud 2.

In a new terminal, start node 4 on cloud 2:

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$ cockroach start \
--insecure \
--locality=cloud=2 \
--store=cloud2node4 \
--host=localhost \
--port=26260 \
--http-port=8083 \
--cache=100MB \
--join=localhost:26257,localhost:26258,localhost:26259

In a new terminal, start node 5 on cloud 2:

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$ cockroach start \
--insecure \
--locality=cloud=2 \
--store=cloud2node5 \
--host=localhost \
--port=25261 \
--http-port=8084 \
--cache=100MB \
--join=localhost:26257,localhost:26258,localhost:26259

In a new terminal, start node 6 on cloud 2:

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$ cockroach start \
--insecure \
--locality=cloud=2 \
--store=cloud2node6 \
--host=localhost \
--port=25262 \
--http-port=8085 \
--cache=100MB \
--join=localhost:26257,localhost:26258,localhost:26259

Step 8. Watch data balance across all 6 nodes

Back in the Admin UI, hover over the Replicas per Node graph again. Because you used --locality to specify that nodes are running on 2 clouds, you'll see an approximately even number of replicas on each node, indicating that CockroachDB has automatically rebalanced replicas across both simulated clouds:

CockroachDB Admin UI

Note that it takes a few minutes for the Admin UI to show accurate per-node replica counts on hover. This is why the new nodes in the screenshot above show 0 replicas. However, the graph lines are accurate, and you can click View node list in the Summary area for accurate per-node replica counts as well.

Step 9. Migrate all data to "cloud 2"

So your cluster is replicating across two simulated clouds. But let's say that after experimentation, you're happy with cloud vendor 2, and you decide that you'd like to move everything there. Can you do that without interruption to your live client traffic? Yes, and it's as simple as running a single command to add a hard constraint that all replicas must be on nodes with --locality=cloud=2.

In a new terminal, edit the default replication zone:

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$ echo 'constraints: [+cloud=2]' | cockroach zone set .default --insecure --host=localhost -f -

Step 10. Verify the data migration

Back in the Admin UI, hover over the Replicas per Node graph again. Very soon, you'll see the replica count double on nodes 4, 5, and 6 and drop to 0 on nodes 1, 2, and 3:

CockroachDB Admin UI

This indicates that all data has been migrated from cloud 1 to cloud 2. In a real cloud migration scenario, at this point you would update the load balancer to point to the nodes on cloud 2 and then stop the nodes on cloud 1. But for the purpose of this local simulation, there's no need to do that.

Step 11. Stop the cluster

Once you're done with your cluster, stop YCSB by switching into its terminal and pressing CTRL-C. Then do the same for HAProxy and each CockroachDB node.

Tip:
For the last node, the shutdown process will take longer (about a minute) and will eventually force kill the node. This is because, with only 1 node still online, a majority of replicas are no longer available (2 of 3), and so the cluster is not operational. To speed up the process, press CTRL-C a second time.

If you don't plan to restart the cluster, you may want to remove the nodes' data stores and the HAProxy config file:

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$ rm -rf cloud1node1 cloud1node2 cloud1node3 cloud2node4 cloud2node5 cloud2node6 haproxy.cfg

What's Next?

Use a local cluster to explore these other core CockroachDB benefits:

You may also want to learn other ways to control the location and number of replicas in a cluster:



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