solr

Multi Core Apache Solr on Ubuntu 10.04 for Drupal with Auto Provisioning

Apache Solr is an excellent full text index search engine based on Lucene. Solr is increasingly being used in the Drupal community for search. I use it for search for a lot of my projects. Recently Steve Edwards at Drupal Connect blogged about setting up a mutli core Solr server on Ubuntu 9.10 (aka Karmic). Ubuntu 10.04LTS was released a couple of months ago and it makes the process a bit easier, as Apache Solr 1.4 has been packaged. An additional advantage of using 10.04LTS is that it is supported until April 2015, whereas suppport for 9.10 ends in 10 months - April 2011.

As an added bonus in this howto you will be able to auto provision solr cores just by calling the right URL.

In this tutorial I will be using Jetty rather than tomcat which some tutorials recommend, as Jetty performs well and generally uses less resources.

Install Solr and Jetty

Installing jetty and Solr just requires a simple command

$ sudo apt-get install solr-jetty openjdk-6-jdk

This will pull down Solr and all of the dependencies, which can be alot if you have a very stripped down base server.

Configuring Jetty

Configuring Jetty is very straight forward. First we backup the existing /etc/default/jetty file like so:

sudo cp -a /etc/default/jetty /etc/default/jetty.bak

Then simply change your /etc/default/jetty to be like this (the changes are highlighted):

# Defaults for jetty see /etc/init.d/jetty for more

# change to 0 to allow Jetty to start
NO_START=0
#NO_START=1

# change to 'no' or uncomment to use the default setting in /etc/default/rcS 
VERBOSE=yes

# Run Jetty as this user ID (default: jetty)
# Set this to an empty string to prevent Jetty from starting automatically
#JETTY_USER=jetty

# Listen to connections from this network host (leave empty to accept all connections)
#Uncomment to restrict access to localhost
#JETTY_HOST=$(uname -n)
JETTY_HOST=solr.example.com

# The network port used by Jetty
#JETTY_PORT=8080

# Timeout in seconds for the shutdown of all webapps
#JETTY_SHUTDOWN=30

# Additional arguments to pass to Jetty    
#JETTY_ARGS=

# Extra options to pass to the JVM         
#JAVA_OPTIONS="-Xmx256m -Djava.awt.headless=true"

# Home of Java installation.
#JAVA_HOME=

# The first existing directory is used for JAVA_HOME (if JAVA_HOME is not
# defined in /etc/default/jetty). Should contain a list of space separated directories.
#JDK_DIRS="/usr/lib/jvm/default-java /usr/lib/jvm/java-6-sun"

# Java compiler to use for translating JavaServer Pages (JSPs). You can use all
# compilers that are accepted by Ant's build.compiler property.
#JSP_COMPILER=jikes

# Jetty uses a directory to store temporary files like unpacked webapps
#JETTY_TMP=/var/cache/jetty

# Jetty uses a config file to setup its boot classpath
#JETTY_START_CONFIG=/etc/jetty/start.config

# Default for number of days to keep old log files in /var/log/jetty/
#LOGFILE_DAYS=14

If you don't include the JETTY_HOST entry Jetty will only bind to the local loopback interface, which is all you need if your drupal webserver is running on the same machine. If you set the JETTY_HOST make sure you configure your firewall to restrict access to the Solr server.

Configuring Solr

I am assuming you have already installed the Apache Solr module for Drupal somewhere. If you haven't, do that now, as you will need some config files which ship with it.

First we enable the multicore support in Solr by creating a file called /usr/share/solr/solr.xml with the following contents:

<solr persistent="true" sharedLib="lib">
 <cores adminPath="/admin/cores" shareSchema="true" adminHandler="au.com.davehall.solr.plugins.SolrCoreAdminHandler">
 </cores>
</solr>

You need to make sure the file is owned by the jetty user if you want it to be dymanically updated, otherwise change persistent="true" to persistent="false", don't include the adminHandler attribute and don't run the commands below. Also if you want to auto provision cores you will need to download the jar file attached to this post and drop it into the /usr/share/solr/lib directory (which you'll need to create).

sudo chown jetty:jetty /usr/share/solr
sudo chown jetty:jetty /usr/share/solr/solr.xml
sudo chmod 640 /usr/share/solr/solr.xml
sudo mkdir /usr/share/solr/cores
sudo chown jetty:jetty /usr/share/solr/cores

To keep your configuration centralised, symlink the file from /usr/share/solr to /etc/solr. Don't do it the other way, Solr will ignore the symlink.

sudo ln -s /usr/share/solr/solr.xml /etc/solr/

Solr needs to be configured for Drupal. First we backup the existing config file, just in case, like so:

sudo mv /etc/solr/conf/schema.xml /etc/solr/conf/schema.orig.xml
sudo mv /etc/solr/conf/solrconfig.xml /etc/solr/conf/solrconfig.orig.xml

Now we copy the Drupal Solr config files from where you installed the module

sudo cp /path/to/drupal-install/sites/all/modules/contrib/apachesolr/{schema,solrconfig}.xml /etc/solr/conf/

Solr needs the path to exist for each core's data files, so we create them with the following commands:

sudo mkdir -p /var/lib/solr/cores/{,subdomain_}example_com/{data,conf}
sudo chown -R jetty:jetty /var/lib/solr/cores/{,subdomain_}example_com

Each of the cores need their own configuration files. We could implement some hacks to use a common set of configuration files, but that will make life more difficult if we ever have to migrate some of cores. Just copy the common configuration for all the cores:

sudo bash -c 'for core in /var/lib/solr/cores/*; do cp -a /etc/solr/conf/ $core/; done'

If everything is configured correctly, we should just be able to start Jetty like so:

sudo /etc/init.d/jetty start

If you visit http://solr.example.com:8080/solr/admin/cores?action=STATUS you should get some xml that looks something like this:

<?xml version="1.0" encoding="UTF-8"?>
<response>
	<lst name="responseHeader">
		<int name="status">0</int>
		<int name="QTime">0</int>
	</lst>
	<lst name="status"/>
</response>

If you get the above output everything is working properly

If you enabled auto provisioning of Solr cores, you should now be able to create your first core. Point your browser at http://solr.example.com:8080/solr/admin/cores?action=CREATE&name=test1&i... If it works you should get output similar to the following:

<?xml version="1.0" encoding="UTF-8"?>
<response>
	<lst name="responseHeader">
		<int name="status">0</int>
		<int name="QTime">1561</int>
	</lst>
	<str name="core">test1</str>
	<str name="saved">/usr/share/solr/solr.xml</str>
</response>

I would recommend using identifiable names for your cores, so for davehall.com.au I would call the core, "davehall_com_au" so I can easily find it later on.

Security Note: As anyone who can access your server can now provision solr cores, make sure you restrict access to port 8080 to only allow access from trusted IP addresses.

For more information on the commands available, refer to the Solr Core Admin API documenation on the Solr wik.

Next in this series will be how to use this auto provisioning setup to allow aegir to provision solr cores as sites are created.

Solr Replication, Load Balancing, haproxy and Drupal

I use Apache Solr for search on several projects, including a few using Drupal. Solr has built in support for replication and load balancing, unfortunately the load balancing is done on the client side and works best when using a persistent connection, which doesn't make a lot of sense for php based webapps. In the case of Drupal, there has been a long discussion on a patch in the issue queue to enable Solr's native load balancing, but things seem to have stalled.

In one instance I have Solr replicating from the master to a slave, with the plan to add additional slaves if the load justifies it. In order to get Drupal to write to the master and read from either node I needed a proxy or load balancer. In my case the best lightweight http load balancer that would easily run on the web heads was haproxy. I could have run varnish in front of solr and had it do the load balancing but that seemed like overkill at this stage.

Now when an update request hits haproxy it directs it to the master, but for reads it balances the requests between the 2 nodes. To get this setup running on ubuntu 9.10 with haproxy 1.3.18, I used the following /etc/haproxy/haproxy.cfg on each of the web heads:

global
    log 127.0.0.1   local0
    log 127.0.0.1   local1 notice
    maxconn 4096
    nbproc 4
    user haproxy
    group haproxy
    daemon

defaults
    log     global
    mode    http
    option  httplog
    option  dontlognull
    retries 3
    maxconn 2000
    balance roundrobin
    stats enable
    stats uri /haproxy?stats

frontend solr_lb
    bind localhost:8080
    acl master_methods method POST DELETE PUT
    use_backend master_backend if master_methods
    default_backend read_backends

backend master_backend
    server solr-a 192.168.201.161:8080 weight 1 maxconn 512 check

backend slave_backend
    server solr-b 192.168.201.162:8080 weight 1 maxconn 512 check

backend read_backends
    server solr-a 192.168.201.161:8080 weight 1 maxconn 512 check
    server solr-b 192.168.201.162:8080 weight 1 maxconn 512 check

To ensure the configuration is working properly run

wget http://localhost:8080/solr -O -
on each of the web heads. If you get a connection refused message haproxy may not be running. If you get a 503 error make sure solr/jetty/tomcat is running on the solr nodes. If you get some html output which mentions Solr, then it should be working properly.

For Drupal's apachesolr module to use this configuration, simply set the hostname to localhost and the port to 8080 in the module configuration page. Rebuild your search index and you should be right to go.

If you had a lot of index updates then you could consider making the master write only and having 2 read only slaves, just change the IP addresses to point to the right hosts.

For more information on Solr replication refer to the Solr wiki, for more information on configuring haproxy refer to the manual. Thanks to Joe William and his blog post on load balancing couchdb using haproxy which helped me get the configuration I needed after I decided what I wanted.