Wednesday, November 16, 2011

boost on centos (vs. on ubuntu)

You'd think porting a C++ program from one 64-bit linux to another would be trivial. But, no. A program developed with no issues on Ubuntu 10.04 was a lot of trouble to get to compile on Centos 5.6.
But get it to compile I did... read on for the secret words you have to utter...

First thing I did was:
   yum erase boost boost-devel

This got rid of the very old 1.33 library. I then ran this:

  yum install boost141 boost141-devel boost141-program-options boost141-regex boost141-thread boost141-system

I then had to hack the makefile to add this to my CFLAGS:

That got me compiling. But not linking. I changed my LDFLAGs to look like this but still it would not link:
  -L/usr/lib64/boost141 -lboost_regex -lboost_program_options -lboost_system -lboost_thread

I played around with various -L settings, until I had a breakthrough. I noticed the above line complained with:
  /usr/bin/ld: cannot find -lboost_thread

But some different -L settings instead gave me:
  /usr/bin/ld: cannot find -lboost_regex

Blink and you miss it, and indeed I had. My above line was linking with most of Boost, just not boost_thread. In other words, I was really close and hadn't realized it. A bit more poking around discovered that Ubuntu calls it "boost_thread", while Centos calls it "boost_thread-mt" (careful, the first one is an underline, the second one is a hyphen). So, the final magic line for Centos was:

  -L/usr/lib64/boost141 -lboost_regex -lboost_program_options -lboost_system -lboost_thread-mt
NOTE: I did not do any post-installation steps after the yum install steps. I saw some people suggesting copying files from one place to another but I did not need to. (Also, -L/usr/lib64 should be sufficient, as every thing is symlinked; maybe even the -L flag is not needed at all... but I'm in the "If it ain't broke." mindset now, so no more experimentation for me!)

Saturday, November 12, 2011

Actual costs: rackspace cloud

A few months back I decided to put a 24/7 script on a Rackspace Cloud instance, instead of the more obvious Amazon EC2 choice. The reason at the time was my needs were low CPU but relatively high bandwidth and diskspace usage and it worked out cheaper.

Now I've had a few invoices in I am relieved to say there was no catch. My past three invoices have been $11.99, $11.99 and $12.20 (USD). This is for a minimal CPU spec (256MB, 1.6% of a quad core CPU, 10GB disk), 1.1 to 1.3 GB/month of outgoing bandwidth each month (there is no charge for incoming bandwidth), and cloud storage rising from 4 to 8GB. 90% of the monthly cost is for the machine, and the cloud storage has risen from $0.63 to $1.15. The bandwidth is not costing much at all.

In contrast on Amazon EC2, the micro instance would cost $15.65 (including $1 for 10GB of EBS storage), while a small instance would cost $62.25/month, of which $0.03 is the bandwidth usage. (The first year of that micro instance would be free if you are a new customer, but I am not.)

So, at the CPU bottom-end, Rackspace is winning on cost. The other feature of Rackspace Cloud that I love is there is an automatic daily backup of the full disk image, and that backup is stored in the cloud storage. (Storing that backup is basically all my $1/month cloud storage costs.)

What do I not like? I keep using up my 10GB disk space. But there seems no way to move to 20GB without doubling the CPU spec and doubling the monthly cost; with Amazon micro I'd just increase the EBS storage space. With an Amazon small instance I'd get 160GB and would not care.

What do I not like about Rackspace and Amazon? It is that you just get a basic linux distro. You have to spend time installing, configuring and maintaining. And the configuration is not trivial; I've kept a log of all I've had to do, and it includes things like moving ssh off of port 22, setting up an iptables firewall, installing a mail server (not a POP server, just enough so I can *send* email alerts), and writing my own low-diskspace email alert script. The latter was done just the other day after my application broke, yet again, because the machine had run out of disk space.

P.S. As I want 24/7, and have not mentioned the need to scale, what about cheaper shared hosting? Well, I couldn't find a VPS, that gives me root access and no restrictions, for under $10/month. It seems Rackspace is winning that fight too?

(2012-08-15 UPDATE: Rackspace are stopping their minimal server config: no more 256MB option in their "nextgen" V2 API. Also scheduled images are not available in the V2 API (yet). In other words the two things I pointed out that were good, in the above article, are going! I guess the Rackspace marketing department will have to work out a positive spin on "cutting out our competitive advantage so we look just like the competition now" ;-)

Sunday, November 6, 2011

PHP, Proxies, HTTPS: v2, v3 or v23?!

From a PHP http client, using HTTPS via a proxy, I started getting a "400 bad request" error from Apache. I knew it could work because it worked last week. The apache error log message was:
   Hostname provided via SNI and hostname mytest.local provided via HTTP are different

My first troubleshooting mistake was messing around with server-side settings: I found out what SNI meant, but as far as I could see I wasn't using it. Then, finally, I remembered I could use curl as a test http client, and it was working fine. I removed all my server-side changes and curl was still connecting fine. So now I knew I'd broken something client-side. I added the -v flag to curl to see the exact headers it is sending. We're both sending the same headers.

Finally I remembered I'd changed this line:

The PHP docs give no guidance on which option to choose, but "v23" sounded like it would work with version 2 or version 3, and maybe do all kinds of auto-negotiation behind the scenes. Which had to be a good thing. I'm sure I'd tested after changing, but I must have tested non-HTTPS or without the proxy by mistake. When I changed back to this line, everything worked again:

I hope that helps someone, as google was no use for me (all the hits about the SNI name and HTTP name difference were due to Apache being case-sensitive about the name comparison, which was not the problem here).

By the way if you want to know how to do http connections, with a proxy, using PHP, supporting both HTTP and HTTPS, I've described it here.