Setting up SVN on AWS EC2 instance

Steps to setup the SVN repository on the cloud instance (http://www.ange-agostini.com/blog/it/5-minutes-to-set-up-a-subversion-server-in-the-cloud.html):

Install subversion, apache and mod_dav_svn:

# sudo yum install mod_dav_svn subversion

Edit the Apache configuration file for subversion:

# sudo vi /etc/httpd/conf.d/subversion.conf

Replace subversion.conf content by:

LoadModule dav_svn_module     modules/mod_dav_svn.so
LoadModule authz_svn_module   modules/mod_authz_svn.so
<Location /repos>
   DAV svn
   SVNParentPath /var/www/svn
   # Limit write permission to list of valid users.
   AuthType Basic
   AuthName "Authorization Realm"
   AuthUserFile /var/www/svn-auth/passwd
   AuthzSVNAccessFile  /var/www/svn-auth/access
   Require valid-user
</Location>

Create the directory which will contain the subversion repository:

# sudo mkdir /var/www/svn

Create the directory which will contain the permissions files.

 # sudo mkdir /var/www/svn-auth

Create the permission file:

# sudo vi /var/www/svn-auth/access
[/]
<theUser> = rw

Note: Replace <theUser> by the login you want to use to access your repository.
<theUser> will have read write access to all repositories.
It is possible to setup authorization by group or user for each repository.
Create the password file:

# sudo htpasswd -cb /var/www/svn-auth/passwd <theUser> <thePassword>

Note: Replace <theUser> by the login you want to use to access your repository. Replace <thePassword> by the password you want.
Create a repository (here project1):

# cd /var/www/svn
# sudo svnadmin create project1

Change files authorization:

# sudo chown -R apache.apache /var/www/svn /var/wwws/vn-auth
# chmod 600 /var/wwws/vn-auth/access /var/www/svn-auth/passwd

Start apache web server:

# sudo service httpd start

Note: to restart server use # sudo service httpd restart

Test subversion

Now subversion and apache should work.
Open a web browser and point to the URL : http://<Public DNS of your EC2 instance>/repos/project1
You should be prompted for your credential (Enter <theUser> <thePassword>) before accessing the repository

Subversion client

We are now going to interact with our repository from a windows PC.
If you don’t have a subversion client installed on your PC then you can install one from http://www.sliksvn.com/en/download .
You can test your subversion client from your PC by listing files on your repository:

svn ls http://<Public DNS of your EC2 instance>/repos/project1

The first time we often want to import some files to the repository:

svn import -m "Initial import." <path of the reposity where are the files on your PC> http://<Public DNS of your EC2 instance>/repos/project1

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ANOTHER WAY:

Steps given at https://forums.aws.amazon.com/thread.jspa?messageID=209468:

I signed up for an EC2 free tier tonight intending to use it as a Subversion server. The whole process took a couple of hours to setup, but can be compressed down to just a few minutes. If anybody else is looking to do the same, here is what I did:

1) Create the Linux-flavored micro instance.
2) Give it a Security Group that opens port 3690 to the sources of your choice. The following example allows SVN access from all Internet sources:

• | tcp | 3690 | 3690 | 0.0.0.0/0
• | udp | 3690 | 3690 | 0.0.0.0/0

3) SSH into the micro instance and run the command "sudo yum install subversion".
4) Create the directory to be used for subversion, for example "/home/ec2-user/svn".
5) Enter "svnadmin create /home/ec2-user/svn" (or whichever path you specified).
6) Edit two files: svnserve.conf and passwd both found in the "conf" directory of your newly created repository source.
In svnserve.conf, unremark the lines for "anon-access" (but change from "read" to "none") and "auth-access". Additionally, unremark the "password-db = passwd" line, but don't change it, and unremark the "realm =" line, providing a realm name of your choice.
In the passwd file, simply add a line entry with the user name(s) and password(s) to be used for access.
7) Finally, run "svnserve -d -r /home/ec2-user/svn" (or again, whichever path you specified) to kick off the instance.

Your Subversion server should now be available at the URL: svn://<yourinstancehostorip>/

Keep in mind the security for this quick and dirty setup is very minimal, and the daemon has not been configured for automatic startup at this point.

Reading:

http://jonathanhui.com/install-configure-subversion-ec2-amazon-linux

Find all contiguous sub-arrays whose sum is zero.

For example:

i/p: 1,2,3,-3,-2,-1
o/p: [2,3], [1,4], [0,5]

You can do a running sum of all the array elements to get the tmp[]:
=> 1 3 6 3 1 0

Now in this array you need to find all duplicates,triplets etc.. All such pairs represent indices of numbers between which the sum of sub-array is zero.

Now to find the duplicates, we can store the tmp[] values as the key in the hashmap with the array index as the values. So, all indices which fall to same key gives us the solution.

How to design a web forum

This was asked to me as a design question in amazon telephonic round. The interviewer wanted to know the DB design and the web-app design for a forum which supports around 100K users with the following use-cases:


 -Sign up
- Posting
- Replying
- Searching [keywords + dates based]

I told him we could have following DB schemas:


Thread [tid, subject, date]
Post [pid, tid, uid, msg, datetime ]
User [uid, role, emailid, password_hash ...]
Role [rid, list flags(for permisssion etc.)...]

The plain DB solves the use cases for Sign-up, posting and replying but could become a bottle neck for search if we run a search query based on query in the Post table (with a where clause as 'like "%keyword%"). So, for improving the performance of this, i suggested running an independent background process which parses the msgs in the post table and stores the important keywords from this messsage in the  independent datastore/B-Tree structure to be able to index the keywords for faster searches. The corresponding value for the keywords is the 'pid' (post id) in the table. This should improve the performance of the query. the interviewer seemed to have liked the proposal. Let me know if you guys can think of a better strategy for faster searches.

After this he wanted me to move to the Java side and explain the design there. I told that we would make similar classes/objects like the tables above, define relationship between those classes and then define the operations on these classes.
For components, I told him i would use the MVC architecture, where the views would be JSPs and Controller would be the interacting servlets which would extract data from the views, call the business logic from the Model and then fill the results in a new view which is returned to the user. He asked me to delve a little deeper into the Model components. I told this would basically have two main layers one is DAO (which interacts with the DB) and other is the service layer (which is called by the controller and internally calls the DAO classes for DB interaction). The service classes would be using the above set of objects.
PS: I wasn't very comfortable with the component design part, so any comments are welcome.