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Clean up docker-faq.adoc (#2277)
Co-authored-by: Jeb Nix <[email protected]>
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‎solr/solr-ref-guide/modules/deployment-guide/pages/docker-faq.adoc‎

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== How do I persist Solr data and config?
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Your data is persisted already, in your container's filesystem.
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If you `docker run`, add data to Solr, then `docker stop` and later `docker start`, then your data is still there.
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The same is true for changes to configuration files.
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Equally, if you `docker commit` your container, you can later create a new
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container from that image, and that will have your data in it.
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For some use-cases it is convenient to provide a modified `solr.in.sh` file to Solr.
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For example to point Solr to a ZooKeeper host:
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[source,bash]
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----
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docker create --name my_solr -P solr
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docker cp my_solr:/opt/solr/bin/solr.in.sh .
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sed -i -e 's/#ZK_HOST=.*/ZK_HOST=cylon.lan:2181/' solr.in.sh
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docker cp solr.in.sh my_solr:/opt/solr/bin/solr.in.sh
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docker start my_solr
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# With a browser go to http://cylon.lan:32873/solr/#/ and confirm "-DzkHost=cylon.lan:2181" in the JVM Args section.
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----
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But usually when people ask this question, what they are after is a way
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to store Solr data and config in a separate https://docs.docker.com/userguide/dockervolumes/[Docker Volume].
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That is explained in the next two questions.
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Solr's Docker image is pre-configured with container path `/var/solr/` as a https://docs.docker.com/storage/volumes/[volume].
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What this means is that all index data, log files and other variable data will be
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persisted on the Docker host, even if you remove the container instance.
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== How can I mount a host directory as a data volume?
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This is useful if you want to inspect or modify the data in the Docker host
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when the container is not running, and later easily run new containers against that data.
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This is indeed possible, but there are a few gotchas.
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Solr stores its core data in the `server/solr` directory, in sub-directories for each core.
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The `server/solr` directory also contains configuration files that are part of the Solr distribution.
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Now, if we mounted volumes for each core individually, then that would interfere with Solr trying to create those directories.
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If instead we make the whole directory a volume, then we need to provide those configuration files in our volume, which we can do by copying them from a temporary container.
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For example:
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By default Solr's volume is persisted in Docker's default storage location on the host.
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On Linux systems this is `/var/lib/docker/volumes`. This is the recommended way to
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store Solr's data. You have flexibility to use a bind mount host folder as well:
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[source,bash]
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----
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# create a directory to store the server/solr directory
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mkdir /home/docker-volumes/mysolr1
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# make sure its host owner matches the container's solr user
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sudo chown 8983:8983 /home/docker-volumes/mysolr1
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# copy the solr directory from a temporary container to the volume
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docker run -it --rm -v /home/docker-volumes/mysolr1:/target solr cp -r server/solr /target/
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# pass the solr directory to a new container running solr
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SOLR_CONTAINER=$(docker run -d -P -v /home/docker-volumes/mysolr1/solr:/opt/solr/server/solr solr)
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# create a new core
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docker exec -it --user=solr $SOLR_CONTAINER solr create -c gettingstarted
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# check the volume on the host:
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ls /home/docker-volumes/mysolr1/solr/
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# configsets gettingstarted README.txt solr.xml zoo.cfg
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docker run --rm -p 8983:8983 -v $(pwd)/myData:/var/solr/ solr:9-slim
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----
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Note that if you add or modify files in that directory from the host, you must `chown 8983:8983` them.
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== How can I use a Data Volume Container?
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You can avoid the concerns about UID mismatches above, by using data volumes only from containers.
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You can create a container with a volume, then point future containers at that same volume.
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This can be handy if you want to modify the solr image, for example if you want to add a program.
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By separating the data and the code, you can change the code and re-use the data.
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But there are pitfalls:
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* if you remove the container that owns the volume, then you lose your data.
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Docker does not even warn you that a running container is dependent on it.
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* if you point multiple solr containers at the same volume, you will have multiple instances
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write to the same files, which will undoubtedly lead to corruption
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* if you do want to remove that volume, you must do `docker rm -v containername`;
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if you forget the `-v` there will be a dangling volume which you can not easily clean up.
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Here is an example:
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[source,bash]
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----
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# create a container with a volume on the path that solr uses to store data.
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docker create -v /opt/solr/server/solr --name mysolr1data solr /bin/true
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# pass the volume to a new container running solr
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SOLR_CONTAINER=$(docker run -d -P --volumes-from=mysolr1data solr)
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# create a new core
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docker exec -it --user=solr $SOLR_CONTAINER solr create -c gettingstarted
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# make a change to the config, using the config API
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docker exec -it --user=solr $SOLR_CONTAINER curl http://localhost:8983/solr/gettingstarted/config -H 'Content-type:application/json' -d '{
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"set-property" : {"query.filterCache.autowarmCount":1000},
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"unset-property" :"query.filterCache.size"}'
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# verify the change took effect
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docker exec -it --user=solr $SOLR_CONTAINER curl http://localhost:8983/solr/gettingstarted/config/overlay?omitHeader=true
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# stop the solr container
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docker exec -it --user=solr $SOLR_CONTAINER bash -c 'cd server; java -DSTOP.PORT=7983 -DSTOP.KEY=solrrocks -jar start.jar --stop'
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# create a new container
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SOLR_CONTAINER=$(docker run -d -P --volumes-from=mysolr1data solr)
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# check our core is still there:
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docker exec -it --user=solr $SOLR_CONTAINER ls server/solr/gettingstarted
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# check the config modification is still there:
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docker exec -it --user=solr $SOLR_CONTAINER curl http://localhost:8983/solr/gettingstarted/config/overlay?omitHeader=true
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----
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But this is both dependent on the host operating system and may run into different kind
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of file system permission issues.
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== Can I use volumes with SOLR_HOME?
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Solr supports a SOLR_HOME environment variable to point to a non-standard location of the Solr home directory.
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You can use this in Solr docker, in combination with volumes:
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[source,bash]
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----
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docker run -it -v $PWD/mysolrhome:/mysolrhome -e SOLR_HOME=/mysolrhome solr
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----
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This does need a pre-configured directory at that location.
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To make this easier, Solr docker supports a INIT_SOLR_HOME setting, which copies the contents
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from the default directory in the image to the SOLR_HOME (if it is empty).
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While you could re-define `SOLR_HOME` inside the container, we instead recommend you
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to use the existing `SOLR_HOME` defined at `/var/solr/`, see above. You can give the
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volume a meaningful name instead of the auto generated hash, example name `solrData`:
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[source,bash]
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mkdir mysolrhome
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sudo chown 8983:8983 mysolrhome
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docker run -it -v $PWD/mysolrhome:/mysolrhome -e SOLR_HOME=/mysolrhome -e INIT_SOLR_HOME=yes solr
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docker run --rm -p 8983:8983 -v solrData:/mysolrhome solr:9-slim
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NOTE: If SOLR_HOME is set, the "solr-precreate" command will put the created core in the SOLR_HOME directory
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rather than the "mycores" directory.
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== Can I run ZooKeeper and Solr clusters under Docker?
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At the network level the ZooKeeper nodes need to be able to talk to each other,
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Used together, you can implement static addresses.
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See the xref:docker-networking.adoc[] for more information.
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== Can I run ZooKeeper and Solr with Docker Links?
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Docker's https://docs.docker.com/engine/userguide/networking/default_network/dockerlinks/[Legacy container links] provide a way to
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pass connection configuration between containers.
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It only works on a single machine, on the default bridge.
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It provides no facilities for static IPs.
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Note: this feature is expected to be deprecated and removed in a future release.
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So really, see the "Can I run ZooKeeper and Solr clusters under Docker?" option above instead.
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But for some use-cases, such as quick demos or one-shot automated testing, it can be convenient.
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Run ZooKeeper, and define a name so we can link to it:
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[source,bash]
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docker run --name zookeeper -d -p 2181:2181 -p 2888:2888 -p 3888:3888 jplock/zookeeper
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----
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Run two Solr nodes, linked to the zookeeper container:
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[source,bash]
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docker run --name solr1 --link zookeeper:ZK -d -p 8983:8983 \
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solr \
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bash -c 'solr start -f -z $ZK_PORT_2181_TCP_ADDR:$ZK_PORT_2181_TCP_PORT'
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docker run --name solr2 --link zookeeper:ZK -d -p 8984:8983 \
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solr \
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bash -c 'solr start -f -z $ZK_PORT_2181_TCP_ADDR:$ZK_PORT_2181_TCP_PORT'
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----
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Create a collection:
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[source,bash]
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docker exec -i -t solr1 solr create \
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-c gettingstarted -shards 2 -p 8983
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----
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Then go to `+http://localhost:8983/solr/#/~cloud+` (adjust the hostname for your docker host) to see the two shards and Solr nodes.
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== How can I run ZooKeeper and Solr with Docker Compose?
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See the xref:solr-in-docker.adoc#docker-compose[docker compose example].

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