apptree's questions

In teaching CS, students submit their code to our server and we compile and run with unit tests. Similar to Codeforces, Codewars, and HackerRank.

How should we be configuring servers for this? Launch a new minimal VM for each code submission? Is there a VM system and linux distribution ideal for this?

Or is there another mechanism for this purpose that is more efficient? Can a user account be configured to handle this safely? We're happy to recycle servers periodically.

We're not tied to any datacenter or service. So happy to use something like AWS Lambda if that's a viable option.

I'm running a Linux c5d.9xlarge instance and wondering what CPU it's using. Amazon's Instance Types webpage states:

C5 and C5d 12xlarge, 24xlarge, and metal instances have the following specs:

• Custom 2nd generation Intel Xeon Scalable Processors (Cascade Lake) with a sustained all core Turbo frequency of 3.6GHz and single core turbo frequency of up to 3.9GHz.

All other C5 and C5d instances have the following specs:

• Custom 2nd generation Intel Xeon Scalable Processors (Cascade Lake) with a sustained all core Turbo frequency of 3.6GHz and single core turbo frequency of up to 3.9GHz or 1st generation Intel Xeon Platinum 8000 series (Skylake-SP) processor with a sustained all core Turbo frequency of up to 3.4GHz, and single core turbo frequency of up to 3.5 GHz.

So I'm curious whether I have a 1st generation Xeon Platinum 8000 series or a 2nd generation Xeon Scalable Processor. How can I check? uname -a just gives me:

$ uname -a
Linux ip-111-11-11-111.us-west-1.compute.internal 4.14.165-131.185.amzn2.x86_64 #1 SMP Wed Jan 15 14:19:56 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux

I'm using the amzn2-ami-hvm-2.0.20200207.1-x86_64-gp2 AMI.

We have 50 computers that students share. Is there an easy way to have student folders on a single drive on the network where each student has a password? Students need to be able to go to any computer and access their password-protected directory.

All the computers are Windows 8, but I'd very much prefer not to have to use a Windows Server.

Right now we connect a USB drive to our router. Works great except the directories are not password-protected. We don't want students deleting other students' work.

I'm happy to use a cloud storage mechanism for this too.

I need to have Tomcat 7 listen on 2 different ports for HTTP requests (the 2nd port makes webapps think it's receiving https requests because that's what's happening on the load balancer). But the 2nd port doesn't work, it just hangs when you try to request a URL from it:

<Connector port="80" protocol="HTTP/1.1" URIEncoding="UTF-8" compression="2048"
           connectionTimeout="20000" 
           redirectPort="443" />
<Connector port="480" protocol="HTTP/1.1" URIEncoding="UTF-8" compression="2048" 
           connectionTimeout="20000"
           redirectPort="443"
           scheme="https" secure="true"/>

Why won't port 480 listen to http requests?

catalina.out shows no issues whatsoever and tomcat is technically listening to port 480:

# tail catalina.out
Nov 4, 2011 4:09:48 PM org.apache.coyote.http11.Http11Protocol init
INFO: Initializing Coyote HTTP/1.1 on http-80
Nov 4, 2011 4:09:48 PM org.apache.coyote.http11.Http11Protocol init
INFO: Initializing Coyote HTTP/1.1 on http-480

# netstat -nlp | grep ":80\|:480"
tcp        0      0 :::480                      :::*                        LISTEN      30046/java          
tcp        0      0 ::ffff:127.0.0.1:8005       :::*                        LISTEN      30046/java          
tcp        0      0 :::8009                     :::*                        LISTEN      30046/java          
tcp        0      0 :::80                       :::*                        LISTEN      30046/java          

I'm currently using New Relic's performance monitoring service. Works great so far, except that I'd like some things automated. I basically just get an email notification when performance is bad or my site is down. If the site is down, I'd like to try restarting the application server (killing the process if necessary, which it is sometimes). If that doesn't work after a period of time, try rebooting the whole machine... I even paid for PagerDuty, which can parse New Relic email notifications and call or SMS me with an escalation procedure for notifications. But it can't run scripts...

Seems like this would be a popular feature of any website monitoring tool... anything good out there?

I've been using a wildcard SSL certificate in Apache Tomcat 7. But now that I have to renew, I see there are these EV (extended verification) SSL certificates where browsers show a nice green bar so users feel better. That would be important for my site, so I want it! But I have multiple subdomains and apparently EV SSL certificates are NOT wildcard by nature. So ok, I have a set number of subdomains, I can just buy a bunch (I definitely need at least 2) EV SSL certificates for each subdomain.

Can I set this up in Tomcat 7 so that there are multiple SSL certificates on 1 web application? It's not a problem for me to assign multiple IP addresses to this machine.

Using CentOS 5 and trying to send an email from the command line (for crontab emailing attachments). mail and mutt execute without errors, but I just never receive any emails. I'm running exim as the local smtp server. My email address is a gmail account.

[root@server ~]# mail -s "hello subject" [email protected] < test_message.txt 
[root@server ~]# mutt -s "hello subject" [email protected] < test_message.txt 
[root@server ~]# 

When I ran mutt by itself, it said there was no /var/spool/mail/root. So I touched it:

[root@server ~]# touch /var/spool/mail/root

still no emails to my gmail account... What do I need to do?

I need to analyze the search engine crawling going on in my site. Is there a good tool for this? I've tried AWStats and Sawmill. But both of those give me very limited insight into the crawling. I need to know information like how many unique/distinct webpages in a section of my site was crawled by a specific crawler within a time period.

Google analytics doesn't track crawling at all due to its javascript tracking mechanism.

I periodically need to make changes to tables in mysql 5.1, mostly adding columns. Very simple with the alter table command. But my tables have up to 40 million rows now and they are growing fast... So those alter table commands take several hours. In a couple months they'll take days I'm guessing.

Since I'm using amazon RDS, I can't have slave servers to play with and then promote to master. So my question is if there's a way to do this with minimal downtime? I don't mind an operation taking hours or even days if users can still use the db of course... Can they at least read while columns are being added? What happens if my app tries to write? Insert or update? If it fails immediately that's actually not so bad, if it just hangs and causes problems for the db server that's a big problem..

This must be a fairly common scaling issue, everyone needs to add columns.. What's typically done to a production db? Slave -> master migration?

Update - I forgot to mention I'm using the innodb storage engine

I'm trying to run the simple django tutorial on my windows 7 machine after having just read the python tutorial. But it complains, "django.core.exceptions.ImproperlyConfigured: Error loading MySQLdb module: No module named MySQLdb".

So I find out that I need a module called MySQLdb. However, very surprisingly, this is difficult to install on windows. I need a C compiler among other things and the README states, "I don't do Windows... Don't ask me for help with Windows because I can't help you." After some googling I find this site which has binaries for old versions (2.5 and 2.6) of python, but no binaries for python 2.7.

This makes me think python was not such a good choice for an easy script/web platform... I can't imagine RoR is anything but easy for a hello world with mysql...

So what should I do? Downgrade Python to an older version to use one of the above prebuilt binaries? Install a c compiler among other things to try and build MySQLdb? Realize that python just doesn't work easily on windows and only use this on a mac/linux machine?