How do I access a Docker volume in a new container?

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eduardopezzi asked Mar 12, '22 Erick Ramirez edited Mar 16, '22

How do I access a Docker volume in a new container?

After update my Cassandra docker container it raised the following error:

CassandraDaemon.java:911 - Fatal configuration error
org.apache.cassandra.exceptions.ConfigurationException: \
    Cannot change the number of tokens from 256 to 16

I am using cassandra:latest image, and probably its updated its version, and after that the server shutdown every time I try to run it again.

docker

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Answer 1 · 2022-03-12T14:39:56Z

steve.lacerda answered Mar 12, '22 eduardopezzi commented Mar 13, '22

It sounds like your cassandra.yaml was updated whenever you ran your update. Check the num_tokens value to verify it’s the same as before you did your update.

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eduardopezzi commented · Mar 12, 2022 at 06:27 PM

Indeed, but as it is a container I was struggling to use the console as the container shutdown all the time. I manage to stop doing that and edit cassandra.yaml

Thank you

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Answer 2 · 2022-03-16T05:57:16Z

Erick Ramirez answered Mar 16, '22 Erick Ramirez edited Mar 16, '22

We do not recommend updating a Cassandra container to a newer version. Cassandra 4.0+ is pre-configured with a new default of 16 virtual nodes (CASSANDRA-13701):

num_tokens: 16

Older versions of Cassandra had a default of 256. It is not possible to change the number of tokens allocated to a node once Cassandra has joined a cluster (even for single-node clusters). As you have already discovered, changing the allocated tokens will prevent Cassandra from starting.

You will need to edit the cassandra.yaml in order to allow Cassandra to start. Provided you named your container cassandra:

$ docker ps -a
CONTAINER ID  IMAGE      COMMAND  CREATED  STATUS  PORTS              NAMES
788db79a03d3  cassandra  ...      ...      Up      7000-7001/tcp,...  cassandra

you can view the cassandra container's configuration with:

$ docker inspect cassandra

and you will see that the configuration directory is set to:

                "CASSANDRA_CONF=/etc/cassandra",

Make a local copy of the configuration file:

$ docker cp cassandra:/etc/cassandra/cassandra.yaml .

Edit your local copy then copy the modified version to the the container with:

$ docker cp cassandra.yaml cassandra:/etc/cassandra/cassandra.yaml

Cheers!

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