Host Maven repositories on a Raspberry Pi
Posted on Sunday May 08, 2016 at 11:42PM in General
For a particular project I'm doing, it would be handy to re-use a JAR file in multiple other future projects. Although there are far more simple solutions to this problem, when I read about repository managers in the official Maven documentation, I gave it some thought and decided to try to run one on one of my Raspberry pi mini-computers that was waiting for a problem to be solved
When hosting a Maven repository on the Raspberry pi, next to hosting private repositories that can be accessed by other computers in my network, it can act as a proxy for Maven Central as well. This means that when a computer in my network needs to download a dependency from Maven Central, it will get a cached copy from the Raspberry pi instead. If the dependency is not already in its cache, it will download the dependency from Maven Central (if it is configured to allow this) first.
Looking at the list of available Maven Repository Managers, Apache Archiva caught my eye and decided to give it a try.
Like many other Apache Software Foundation projects that I follow, Archiva is a project with light traffic and not a lot of new releases lately, this is not necessarily a bad thing though, hopefully this is a sign that the current version is generally considered stable.<.p>
What I saw when looking up for more information, impressed me. The web user-interface looks really user-friendly and nice.
Running Archiva in Standalone mode or Servlet container?
Archiva can run in two modes:
- Stand-alone (a script can be started on the console, that will start an embedded web-server)
- Run inside a Servlet container (Apache Tomcat) or dedicated Java EE application server (Glassfish, JBoss/Wildfly, Oracle WebLogic...)
Let's take a look at both options
Standalone mode on the Raspberry pi
At first I tried running Archiva in stand-alone mode, assuming this would be ideal for the Raspberry pi.
I had many issues along the way, which all had to do with Archiva's dependency of an out-dated version of Java Service Wrapper by Tanuki Software. As I understand Service Wrapper is a component that lets Java applciations run as Linux daemons and Windows services. Due to licensing issues, the Archiva team can not upgrade this component to a more up to date version.
Blogger Ti-80 - almost exactly three years ago - made a blog post about running Archiva on the Raspberry pi and it seems all problems can be solved by manually building the project and replacing binaries.
I decided to not follow this route and run it in a servlet container. I reasoned I'll probably want to run additional servlets on this Raspberry pi in the future anyway. And Adam Bien convinced me that Tomcat's memoy consumption is not as excessive as some people seem to think.
Running inside Servlet Container
Here are the steps that I took to get this up and running. I did not follow the documentation exactly, as I have some other conventions. Feel free to disagree with me and use their instructions! Note that I use a Raspberry pi 2 (4 cores and 1GB of internal memory), I have not tried this on other models.
The official installation guide is here.
- Login with SSH to your Raspberry pi, I used the built-in pi user (you did change its default password, didn't you?! )
Create a dedicated Linux user for running Tomcat:
Follow the prompts, then change active user to "tomcat"
Let's create directories and download Tomcat and Archiva
Visit the TomCat homepage and look for the download link of the .tar.gz release of the currently stable version. At the time of this writing this was 8.0.33
(replace "URL-TO-TOMCAT.tar.gz" with the download URL)
tar xvfz ./apache-tomcat-X.Y.Z.tar.gz
(replace "apache-tomcat-X.Y.Z.tar.gz" with downloaded file)
mv ./apache-tomcat-X.Y.Z ~/tomcat
(move the created directory, not the downloaded tar.gz file!, to the home directory)
Visit the Archiva homepage and look for the download link of the WAR release of the currently stable version. At the time of this writing this was 2.2.0
wget URL-TO-ARCHIVA.war (replace "URL-TO-ARCHIVA.war" with the download URL)
I create a dedicated directory for Archiva and do not place it in the Tomcat home directory (which the Installation Guide suggests). I don't want to pollute Tomcat home directory with Archiva related files. This is a debatable decision, as some dedicated TomCat configuration files will be required to run Archiva anyway.
mkdir -p webapps/archiva
cp ~/downloads/*archiva* ./
Let's create Tomcat context configuration XML file.
mkdir -p Catalina/localhost
(Install nano if it could not be found: apt-get install nano)
Enter following code in Nano
(Substitute the docBase path with the full path to your downloaded war file)
<?xml version="1.0" encoding="UTF-8"?> <Context path="/archiva" docBase="/home/tomcat/webapps/archiva/war/apache-archiva-2.2.0.war"> <Resource name="jdbc/users" auth="Container" type="javax.sql.DataSource" username="sa" password="" driverClassName="org.apache.derby.jdbc.EmbeddedDriver" url="jdbc:derby:/home/tomcat/webapps/archiva/db/users;create=true" /> <Resource name="mail/Session" auth="Container" type="javax.mail.Session" mail.smtp.host="localhost"/> </Context>
Press CTRL+X , then Y to exit.
A bit annoyingly, you'll need to install some dependencies in the "lib" directory of Tomcat
You could download the Archiva .zip release and get it from them, but you could also download the files from mvnrepository.com, what we'll do here. I've chosen the exact versions used by the current Archiva stable version to prevent conflicts. We could regret this later, when installing applications that require newer versions... .
Check the installation guide to see if the version numbers mentioned here still match with the latest version!
Vist http://central.maven.org/maven2/javax/activation/activation/1.1/activation-1.1.jar and find the "Download JAR" button. Copy the link URL.
wget LINK-TO-ACTIVATION-1-1.JAR (replace with full link to activation-1-1.jar)
Vist http://mvnrepository.com/artifact/javax.mail/mail/1.4 and find the "Download JAR" button. Copy the link URL.
wget LINK-TO-MAIL-1-4.JAR (replace with full link to mail-1.4.jar)
Vist http://mvnrepository.com/artifact/org.apache.derby/derby/10.12.1.1 and find the "Download JAR" button. Copy the link URL (manual states newer versions of Derby than mentioned in the documentation should work fine).
wget LINK-TO-DERBY.JAR (replace with full link to Derby jar file)
Finally create a start script that will boot Tomcat and additionally sets some required environmental variables.
Add the following content:
export CATALINA_OPTS="-Dappserver.home=/home/tomcat/webapps/archiva -Dappserver.base=/home/tomcat/webapps/archiva" /home/tomcat/tomcat/bin/startup.sh
Press CTRL+X , then Y to exit.
chmod +x ./startup.sh
- Run the script:
On the computer you used to log in to Raspberry pi, start your browser (so do not run the browser on your Raspberry pi), go to:
(replace IP_ADDRESS_RASPBERRY_PI with the correct ip address or host name)
If everything goes well, after a few seconds you should see a welcome screen, with a button at the top right side to create an admin user. Note that booting can take some time.
On problems, you'd get a simple 404 screen. In that case you'll have to look at the log files of Tomcat and try to determine what is wrong, usually something's wrong with one of the paths or dependencies:
nano /home/tomcat/tomcat/logs/localhost.YYYY-MM-DD.log (replace with your current date)
- Create the admin user and follow the prompts.
I should do a future blog post about configuring Archiva, I feel the default settings are good enough to get started.
Configure Maven clients to use Archiva
To get started, let's configure your desktop machine clients to use Archiva to retrieve dependencies of Maven Central from now on only from your Raspberry pi. I advise to not configure your Maven clients on your laptops, unless your Raspberry pi is accessible via the internet, or you have a VPN or something. Otherwise you won't be able to get your dependencies when your Raspberry pi is not on your current network.
Create or edit your Maven settings file from your user directory with your favorite editor,.
On modern Windows machines, this file should be located on:
c:\users\XXX\.m2\settings.xml (replace XXX wityh your username)
On Linux machines, this file is located at:
Make sure the setting.xml file contains at least something like: (but if you have other entries as well, like proxies, etc., make sure to retain them)
<?xml version="1.0" encoding="UTF-8"?>
User-specific configuration for maven. Includes things that should not
be distributed with the pom.xml file, such as developer identity, along with
local settings, like proxy information. The default location for the
settings file is ~/.m2/settings.xml
<settings xmlns="http://maven.apache.org/SETTINGS/1.0.0" xmlnssi="http://www.w3.org/2001/XMLSchema-instance"
Of course, replace RASPBERRY_IP_ADDRESS with your Raspberry pi's IP address.
The <mirrorOf>central</mirrorOf> entry tells Maven to only use your Raspberry pi mirror for Maven Central dependencies. Refer to the Maven documentation for more mirror configuration options. Also make sure to read the corresponding Archiva chapter on this subject.
Now when you build a project, Maven Central repositories will be downloaded from your Raspberry pi, which will automatically download the dependency if it did not have it already in its cache.
Some final thoughts
The (Micro-)SD card from your Raspberry pi can get corrupted when files change very often. So if you very frequently add new dependencies or change versions, it's probably better to attach a external harddrive to your Raspberry pi and make sure the Maven repositories are stored on that hard drive.
If after testing you don't want to use Archiva anymore, simply remove the <mirror>....</mirror> entries from your client's settings.xml and you should be fine.
To shutdown TomCat on your Raspberry, you can use standard ~/tomcat/bin/shutdown.sh script, but remember to start the server, use the script in your home directory, otherwise Archiva won't start because it can not find its home directory.
On my Raspberry pi, less than 250 MB of memory was used to run Linux, Tomcat and Archiva, so I have plenty of room to run other servlets on my Raspberry pi in the future.
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