In this article I will try to explain a weird error that I had to deal with, working with Redis.
The common message of the error is "(error) MOVED 12933 127.0.0.1:30003". Now let's
see when this could happened.
In order to follow me you maybe will need to have Redis, I will also assume that you are
using some UNIX like distro, but you could find out the equivalents command on Windows by yourself.
You are a big boy. In total we only need:
- OS: Ubuntu, Debian, Centos, etc... you got the idea.
Downloading and compiling Redis
The current stable version of Redis is 6.2.6, you could download it
through this link or making use of curl, like this:
curl -sO https://download.redis.io/releases/redis-6.2.6.tar.gz
tar -xf redis-6.2.6.tar.gz
Now you should have a folder called redis-6.2.6, let's position inside of it with
Now we are good to go.
In case you want to run the tests inside the redis code, you could run
make test. There are other parameters that you can pass in the
build, that could be interesting to trying out, but not now.
In case you are in hurry, let me just summarize it to you. You will find this error when you try to use a redis client on a redis cluster,
without specifying on this redis client that you are actually connecting to a redis cluster and not a normal redis node. Of course, if you just
read this sentence could be the case that it makes no sense to you, right? Let's go deeper then.
Reproducing the error
Let's try to reproduce this error without any particular library in any language first, just making use of redis-cli.
Let's run a Redis cluster locally, it will be easy. If you already compiled the source code of redis in the previous setup, you will
notice that there's a folder called
utils. Inside this folder there's another one called
create-cluster, so I'm going to make use
of the script inside this folder to create a cluster, is just the easiest way.
In order to run this scrip you need to be position in the same folder as the script, so let's go into there:
Run the script:
./create-cluster start ./create-cluster create
Yes, like that. Wait what? Is already created? Yep, is code written in C so... A little confusing what they mean by
create, usually the order
create and then
start, but naming is hard.
create command it will ask you Can I set the above configuration? (type 'yes' to accept), so type yes, you are following a
tutorial that's the point.
Now we have our cluster locally running.
How to stop and clean this?
./create-cluster stop ./create-cluster clean
Let's connect to the cluster with redis-cli.
In the previous step you must notice a line like this one in the logs printed on the
./create-cluster create command:
>>> Performing Cluster Check (using node 127.0.0.1:30001)
In my case the port that I will be trying to connect is 30001, but in your case could be any other.
./src/redis-cli -c -p 30001
VERY IMPORTANT HERE
-c option is for
-c Enable cluster mode (follow -ASK and -MOVED re-direction).
So right now we are connecting using the cluster mode, so we won't have any problem, the problem will come later
if we try to make operation with a connection that doesn't have this Cluster mode enabled. I'll comment more on that later.
PING command just to check if everything looks fine,
You should get
PONG as an answer.
Now let's back to business ), I will set several pairs and later I will try to fetch them
127.0.0.1:30001> SET name Lola -> Redirected to slot  located at 127.0.0.1:30002 OK 127.0.0.1:30002> SET name1 Lola -> Redirected to slot  located at 127.0.0.1:30003 OK 127.0.0.1:30003> SET name2 Manolo -> Redirected to slot  located at 127.0.0.1:30001 OK 127.0.0.1:30001> SET name3 Juan OK 127.0.0.1:30001> SET name4 Juan -> Redirected to slot  located at 127.0.0.1:30002 OK 127.0.0.1:30002
Take a look at these logs, yes I'm connected to port 30001 but my pairs, not always were set at that node. In my case
the value for key
name1, on command
SET name1 Lola was located in a slot in node 30003. I will explain more in advance, for now let's just
reproduce the error.
Connecting without cluster mode enabled
Let's try to connect to one of this node without enabling cluster mode, so open another terminal and run a this command:
./src/redis-cli -p 30001
Here the difference is that the option
-c was not supplied.
PING, can we? Yes, we can!
127.0.0.1:30001> PING PONG
Now comes the cool surprise, at the moment you must be thinking like,
"Well I just made PING without problem, so I'm sure that I could retrieve those that I already pushed, right?"
Let's try to retrieve them with GET command,
127.0.0.1:30001> GET name1
127.0.0.1:30001> GET name1 (error) MOVED 12933 127.0.0.1:30003 127.0.0.1:30001>
Enjoy debugging this on your application, is not fun at all really. You start thinking, like, why? I ran the magical command called
everything is fine.
Just to clarify, this is NOT an error of the server, this is YOUR FAULT, for setting up bad your redis client.
Rule of thumb
In general if you are using a redis cluster in your server, you should enabled the cluster mode on your client. There's a lot of alternatives
for this, depending on the Programming Language that you are using. Here is a list from the redis website:
- redis-rb-cluster is a Ruby implementation written by me (@antirez) as a reference for other languages. It is a simple wrapper around the original redis-rb, implementing the minimal semantics to talk with the cluster efficiently.
- redis-py-cluster A port of redis-rb-cluster to Python. Supports majority of redis-py functionality. Is in active development.
- The popular Predis has support for Redis Cluster, the support was recently updated and is in active development.
- The most used Java client, Jedis recently added support for Redis Cluster, see the Jedis Cluster section in the project README.
- StackExchange.Redis offers support for C# (and should work fine with most .NET languages; VB, F#, etc)
- thunk-redis offers support for Node.js and io.js, it is a thunk/promise-based redis client with pipelining and cluster.
- redis-go-cluster is an implementation of Redis Cluster for the Go language using the Redigo library client as the base client. Implements MGET/MSET via result aggregation.
- ioredis is a popular Node.js client, providing a robust support for Redis Cluster.
- The redis-cli utility implements basic cluster support when started with the -c switch.
Related to Golang, the library go-redis, have also support for this.
Until next error guys ).
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