To form a Solr Cluster you will need to install and configure ZooKeeper: see Install and configure a ZooKeeper

By default, Solr configuration will be pushed to ZooKeeper and will be created under the ZooKeeper root znode "/".
To be able to create the Solr configuration under a custom location (ie: "/solr"), you need to use ZooKeeper "chroot".
The usage of ZooKeeper "chroot" is not mandatory but it's considered as a best practice.

If you choose to have Solr configuration created under a custom location, then you have to create manually the "chroot" znode in ZooKeeper.
You can use ZooKeeper Command Line Utilities file "zkCli.sh" to create your "chroot" znode (ie: "/solr"):
$ ${ZK_HOME}/bin/zkCli.sh -server localhost:2181 create /solr

We will install Solr on 2 different hosts: "solrhost1", and "solrhost2"

Assuming we have already installed and configured ZooKeeper. One ZooKeeper instance should be sufficient but we will assume that we have a ZooKeeper Cluster formed of 3 nodes installed on 3 different hosts: "zkhost1", "zkhost2", and "zkhost3"

On each Solr host, do the following:

1. Download and Install Apache Solr
   • Download Apache Solr http://lucene.apache.org/solr/
     
     
   • Extract the file "solr-9.1.1.zip" in the folder you want to install Solr: /opt/solr-9.1.1
     $ unzip solr-9.1.1.zip -d /opt/
     
   • Create a symbolic link of the Solr installation folder:
     $ ln -s /opt/solr-9.1.1/ /opt/solr
     
   • Change the folders permissions (if needed):
     $ chmod -R 755 /opt/solr-9.1.1/ $ sudo chown -R mtitek:mtitek /opt/solr-9.1.1/ $ sudo chown -R mtitek:mtitek /opt/solr
2. Configuration files and environment variables
   ${SOLR_HOME} (or solr.solr.home) represents the path of the Solr home directory: /opt/solr/server/solr

${SOLR_ROOT} represents the path of the Solr installation folder: /opt/solr/
   
   Configuration files:
   ► "${SOLR_HOME}/solr.xml"
   
   Solr home directory ${SOLR_HOME} must contain a solr.xml file, otherwise Solr will fail to start.
   
3. Start Solr
   Start Solr on each Solr host ("solrhost1", "solrhost2")
   $ /opt/solr/bin/solr start -c -z "zkhost1:2181,zkhost2:2181,zkhost3:2181/solr"
   You can omit -z "zkhost1:2181,zkhost2:2181,zkhost3:2181/solr" from the above command if you have defined "ZK_HOST" in "solr.in.sh".
   
   Typically, you can use one of the following options to start Solr:
   
   

   • Specifying a ZooKeeper instance (not recommended to not setting a ZooKeeper chroot ):
     $ /opt/solr/bin/solr start -c -z "zkhost1:2181"
     
   • Specifying a ZooKeeper instance + setting ZooKeeper chroot to "/solr" (the znode "/solr" has to be created first in ZooKeeper):
     $ /opt/solr/bin/solr start -c -z "zkhost1:2181/solr"
     
   • Specifying multiple ZooKeeper instances:
     $ /opt/solr/bin/solr start -c -z "zkhost1:2181,zkhost2:2181,zkhost3:2181/solr"
     
   • Adding additional JVM parameters (start Solr running in SolrCloud mode with 1g max heap size and remote Java debug options enabled):
     $ /opt/solr/bin/solr start -c -m 1g -z "zkhost1:2181,zkhost2:2181,zkhost3:2181/solr" -a "-Xmx1024m -Xdebug -Xrunjdwp:transport=dt_socket,server=y,suspend=n,address=1044"
     

   Access the Solr Admin UI: http://solrhost1:8983/solr
   
   
   
   Notes:
   
   

   • If you are using ZooKeeper "chroot", make sure that the Solr znode is created first in ZooKeeper ("/solr").
     
     Otherwise you will get this error at startup:
     ERROR (main) [ ] o.a.s.c.SolrCore null:org.apache.solr.common.cloud.ZooKeeperException: A chroot was specified in ZkHost but the znode doesn't exist. localhost:2181/solr at org.apache.solr.core.ZkContainer.initZooKeeper(ZkContainer.java:112) at org.apache.solr.core.CoreContainer.load(CoreContainer.java:623) at org.apache.solr.servlet.SolrDispatchFilter.createCoreContainer(SolrDispatchFilter.java:261) at org.apache.solr.servlet.SolrDispatchFilter.init(SolrDispatchFilter.java:181) at org.eclipse.jetty.servlet.FilterHolder.initialize(FilterHolder.java:136) at org.eclipse.jetty.servlet.ServletHandler.lambda$initialize$0(ServletHandler.java:750)
     
   • At startup, Solr will try to upload the "_default" configuration to ZooKeeper ("${SOLR_HOME}/configsets/_default").
     
     
   • Verify that the ZooKeeper instances are up and running, otherwise Solr won't start correctly.
     
     
   • If all ZooKeeper instances, specified in the "-z" parameter, go down, Solr will lose connection with ZooKeeper even if the ZooKeeper ensemble contains other instances that are up and running.
     
     
   • You can specify memory options: -m 512m (default)
     
     
   • On windows, you need to put the ZooKeeper hosts between double quotes: -z "zkhost1:2181,zkhost2:2181,zkhost3:2181/solr"
     
     
4. Stop Solr
   To stop Solr, you need to run the following command on each Solr host ("solrhost1", "solrhost2")
   $ /opt/solr/bin/solr stop
   You can also stop Solr server for which the HTTP listener is bound to the specified port:
   $ /opt/solr/bin/solr stop -p 8983

To form a Solr Cluster you will need to install and configure ZooKeeper: see Install and configure a ZooKeeper Cluster on the same host
We will assume that we have a ZooKeeper Cluster formed of 3 nodes installed on the same host where Solr will be installed.

You have to create manually the znode "/solr" in ZooKeeper.

Extract the content of "solr-9.1.1.zip" file to 2 locations of your choice:
► /opt/solr-i1
► /opt/solr-i2

Running the first Solr instance (port: 8983)
$ /opt/solr-i1/bin/solr start -c -z "localhost:2181,localhost:2182,localhost:2183/solr" -p 8983
Running the second Solr instance (port: 8984)
$ /opt/solr-i2/bin/solr start -c -z "localhost:2181,localhost:2182,localhost:2183/solr" -p 8984
Access the Solr Admin UI: http://localhost:8983/solr



To stop Solr:
$ /opt/solr-i1/bin/solr stop -p 8983
$ /opt/solr-i2/bin/solr stop -p 8984

To form a Solr Cluster you will need to install and configure ZooKeeper: see Install and configure a ZooKeeper Cluster on the same host
We will assume that we have a ZooKeeper Cluster formed of 3 nodes installed on the same host where Solr will be installed.

You have to create manually the znode "/solr" in ZooKeeper.

Extract the content of "solr-9.1.1.zip" file to a location of your choice:
► /opt/solr

Here are the steps to follow:

• You need to create a folder that will hold the configuration for each Solr instance (you can choose any path you want): solr1, solr2, ...
  $ mkdir /opt/solr/solr1 $ mkdir /opt/solr/solr2
  
• On each Solr instance home folder (solr1, solr2, ...), you need to copy the "solr.xml" file from "/opt/solr/server/solr".
  $ cp /opt/solr/server/solr/solr.xml /opt/solr/solr1 $ cp /opt/solr/server/solr/solr.xml /opt/solr/solr2
  
• On each Solr instance home folder (solr1, solr2, ...), you need to create a "logs" directory.
  $ mkdir /opt/solr/solr1/logs $ mkdir /opt/solr/solr2/logs
  
• (Linux) Modify the file /opt/solr/bin/solr:
  if [ -z "$SOLR_LOGS_DIR" ]; then #SOLR_LOGS_DIR="$SOLR_SERVER_DIR/logs" SOLR_LOGS_DIR="${SOLR_HOME}/logs" fi
  
• (Windows) Modify the file solr.cmd: IF [%SOLR_LOGS_DIR%] == [] ( @REM set "SOLR_LOGS_DIR=%SOLR_SERVER_DIR%\logs" set "SOLR_LOGS_DIR=%SOLR_HOME%\logs" )
  

Running the first Solr instance (port: 8983)
$ /opt/solr/bin/solr start -c -z "localhost:2181,localhost:2182,localhost:2183/solr" -p 8983 -s "/opt/solr/solr1"
Running the second Solr instance (port: 8984)
$ /opt/solr/bin/solr start -c -z "localhost:2181,localhost:2182,localhost:2183/solr" -p 8984 -s "/opt/solr/solr2"
To stop Solr:
$ /opt/solr/bin/solr stop -p 8983
$ /opt/solr/bin/solr stop -p 8984
You can also try this command to stop all running Solr servers on a host:
$ /opt/solr-i1/bin/solr stop -all