Admin CentOS

CentOS 6.0 VM ran out of memory

I’m just creating this post to have documented what happened to me personally. I have a CentOS 6.0 image with Amazon AWS. It was based on a minimal image, which I purposefully selected so it wouldn’t be loaded down with junky daemons. Ran fine for a year, then one day nothing!

The details
I think it was up for 400 days consecutive! That’s not necessarily a good idea, but those are the facts. Then over the weekend I could neither ssh nor access its web server. Oh, oh. You’ve got really limited options at that point with a cloud server. I stopped it from the AWS console and then started it. No joy. More drastic action – really the last thing I can do short of abandoning the whole image: Terminate. After some breath-holding moments, and after I remembered to re-associate the elastic IP, it came up. Whew! Now it came up as CentOS v 6.4, which I don’t fully understand, but it works.

I checked the /var/log/messages file for clues as to what happened. There actuially were some pretty good clues. Here is the last of many, many similar lines I observed:

Nov 29 08:39:23 ip-10-114-206-104 kernel: Out of memory: kill process 29076 (httpd) score 107231 or a child
Nov 29 08:39:23 ip-10-114-206-104 kernel: Killed process 31306 (httpd) vsz:264320kB, anon-rss:30852kB, file-rss:312kB
Nov 29 08:39:23 ip-10-114-206-104 kernel: httpd invoked oom-killer: gfp_mask=0x201da, order=0, oom_adj=0
Nov 29 08:39:23 ip-10-114-206-104 kernel: httpd cpuset=/ mems_allowed=0
Nov 29 08:39:23 ip-10-114-206-104 kernel: Pid: 31506, comm: httpd Not tainted 2.6.32-131.17.1.el6.x86_64 #1
Nov 29 08:39:23 ip-10-114-206-104 kernel: Call Trace:
Nov 29 08:39:23 ip-10-114-206-104 kernel: [<ffffffff810c00f1>] ? cpuset_print_task_mems_allowed+0x91/0xb0
Nov 29 08:39:23 ip-10-114-206-104 kernel: [<ffffffff811102bb>] ? oom_kill_process+0xcb/0x2e0
Nov 29 08:39:23 ip-10-114-206-104 kernel: [<ffffffff81110880>] ? select_bad_process+0xd0/0x110
Nov 29 08:39:23 ip-10-114-206-104 kernel: [<ffffffff81110918>] ? __out_of_memory+0x58/0xc0
Nov 29 08:39:23 ip-10-114-206-104 kernel: [<ffffffff81110b19>] ? out_of_memory+0x199/0x210
Nov 29 08:39:23 ip-10-114-206-104 kernel: [<ffffffff81120262>] ? __alloc_pages_nodemask+0x812/0x8b0
Nov 29 08:39:23 ip-10-114-206-104 kernel: [<ffffffff8115473a>] ? alloc_pages_current+0xaa/0x110
Nov 29 08:39:23 ip-10-114-206-104 kernel: [<ffffffff8110d717>] ? __page_cache_alloc+0x87/0x90
Nov 29 08:39:23 ip-10-114-206-104 kernel: [<ffffffff81122bab>] ? __do_page_cache_readahead+0xdb/0x210
Nov 29 08:39:23 ip-10-114-206-104 kernel: [<ffffffff81122d01>] ? ra_submit+0x21/0x30
Nov 29 08:39:23 ip-10-114-206-104 kernel: [<ffffffff8110e9e3>] ? filemap_fault+0x4c3/0x500
Nov 29 08:39:23 ip-10-114-206-104 kernel: [<ffffffff810061af>] ? xen_set_pte_at+0xaf/0x170
Nov 29 08:39:23 ip-10-114-206-104 kernel: [<ffffffff81137204>] ? __do_fault+0x54/0x510
Nov 29 08:39:23 ip-10-114-206-104 kernel: [<ffffffff811377b7>] ? handle_pte_fault+0xf7/0xb50
Nov 29 08:39:23 ip-10-114-206-104 kernel: [<ffffffff81007c4f>] ? xen_restore_fl_direct_end+0x0/0x1
Nov 29 08:39:23 ip-10-114-206-104 kernel: [<ffffffff81006d4b>] ? xen_set_pmd_hyper+0x8b/0xc0

So it ran out of memory. I guess there’s a memory leak somewhere, although another posting I saw hinted at a flaw in the CentOS under paravirtualization. I have no idea.

The interesting thing to me is that the error was ongoing for days. So I had I been watching for it, I could have been pro-active in rebooting my server.

My AWS-hosted CentOS VM gave me a scare when it stopped responding. I had to terminate it. An out-of-memory error in the kernel seems to be the proximate cause.

Admin Hosting Service Linux

Hosting: You Really Can’t beat Amazon Web Services EC2

You want to have your own server hosted by a service provider that’s going to take care of the hard stuff – uninterruptible power, fast pipe to the Internet, backups? That’s what I wanted. In addition I didn’t want to worry about actual, messy hardware. Give me a virtual server any day of the week. I am no hosting expert, but I have some experience and I’d like to share that.

The Details
I’d say chances are about even whether you’d think of Amazon Web Services for the above scenario. I’d argue that Amazon is actually the most competitive service out there and should be at the top of any short list, but the situation wasn’t always so even as recently as February of this year.

You see, Amazon markets itself a bit differently. They are an IaaS (infrastructure as a service) provider. I don’t know who their top competition really is, but AWS (Amazon Web Service) is viewed as both visionary and able to execute by Gartner from a recent report. My personal experience over the last 12 months backs that up. My main point, however, is that hosting a server is a subset of IaaS. I assume that if you want your own server where you get root access, you have the skill set (aided by the vast resources on the Internet including blogs like mine) to install a web server, database server, programming environment, application engines or whatever you want to do with it. You don’t need the AWS utility computing model per se, just a reliable 24×7 server, right? That’s my situation.

I was actually looking to move to “regular” hosting provider, but it turns out to have been a really great time to look around. Some background. I’m currently running such an environment running Ubuntu server 10.10 as a free-tier micro instance. I’ve enjoyed it a lot except one thing. From time to time my server freezes. At least once a month since December. I have no idea why. Knowing that my free tier would be up anyways this month I asked my computer scientist friend “Niz” for a good OS to run a web server and he said CentOS is what I want. It’s basically Redhat Enterprise Linux except you don’t pay Redhat for support.

I looked at traditional hosting providers GoDaddy and Rackspace and 1and1 a bit. I ran the numbers and saw that GoDaddy, with whom I already host my DNS domains, was by far the cost leader. They were also offering CentOS v 5.6 I think RackSpace also had a CentOS offering. I spoke with a couple providers in my own state. I reasoned I wuold keep my business local if the price was within 25% of other offers I could find.

Then, and here’s one of the cool things about IaaS, I fired up a CentOS image at Amazon Elastic Compute Cloud. With utility computing I pay only by the hour so I can experiment cheaply, which I did. Niz said run v 5.6 because all the bugs have been worked out. He hosts with another provider so he knows a thing or two about this topic and many other topics besides. I asked him what version he runs. 5.6. So I fired it up. But you know, it just felt like a giant step backwards through an open source timeline. I mean Perl v 5.8.8 vs Ubuntu’s 5.10.1. Now mind you by this time my version of Ubuntu is itself a year old. Apache version 2.2.3 and kernel version 2.6.18 versus 2.2.16 and 2.6.35. Just plain old. Though he said support would be available for fantastical amount of time, I decided to chuck that image.

Just as I was thinking about all these things Amazon made a really important announcement: prices to be lowered. All of a sudden they were competitive when viewed as a pure hosting provider, never mind all the other features they bring to bear.

I decided I wanted more memory than the 700 MB available to a micro image, and more storage than the 8 GB that tier gives. So a “small” image was the next step up, at 1.7 GB of memory and 160 GB disk space. But then I noticed a quirky thing – the small images only come in 32-bit, not 64-bit unlike all the other tiers. I am so used to 64-bit by now that I don’t trust 32-bit. I want to run what a lot of other people are running to know that the issues have been worked out.

Then another wonderful thing happened – Amazon announced support for 64-bit OSes in their small tier! What timing.

The Comparison Results
AWS lowered their prices by about 35%, a really substantial amount. I am willing to commit up front for an extended hosting because I expect to be in this for the long haul. Frankly, I love having my own server! So I committed to three years small tier, heavy usage after doing the math in order to get the best deal for a 24×7 server. It’s $300 $96 up front and about $0.012$0.027/hour for one instance hour. So that’s about $18 $22/month over three years. Reasonable, I would say. For some reason my earlier calculations had it coming out cheaper. These numbers are as of September, 2013. I was prepared to use GoDaddy which I think is $24/month for a two-year commitment. My finding was that RackSpace and 1and1 were more expensive in turn than GoDaddy. I have no idea how AWS did what they did on pricing. It’s kind of amazing. My local providers? One came in at six times the cost of GoDaddy(!), the other about $55/month. Too bad for them. But I am excited about my new server. I guess it’s a sort of master of my own destiny type of thing that appeals to my independent spirit. Don’t tell Amazon, but really I think they could have easily justified charging a small premium for their hosting, given all the other convenient infrastructure services that are there, ready to be dialed up, say, like a load balancer, snapshots, additional IPs, etc. And there are literally 8000 images to choose from when you are deciding what image (OS) to run. That alone speaks volumes about the choices you have available.

What I’m up to
I installed CentOS 6.0 core image. It feels fresher. It’s based on RedHat 6.0 It’s got Perl v. 5.10.1, kernel 2.6.32, and, once you install it, Apache v 2.2.15. It only came with about 300 packages installed, which is kind of nice, not the usual 1000+ bloated deal I am more used to. And it seems fast, too. Now whether or not it will prove to be stable is an entirely different question and only time will tell. I’m optimistic. But if not, I’ll chuck it and find something else. I’ve got my data on a separate volume anyways which will persist regardless of what image I choose – another nice plus of Amazon’s utility computing model.

A Quick Tip About Additional Volumes
With my micro instance it occupied a full 8 GB so I didn’t have a care about additional disk volumes. On the other hand, my CentOS 6.0 core image is a lean 6 GB. If I’m entitled to 160 GB as part of what I’m paying for, how do I get the access to the remaining 154 GB? I guess you create a volume. Using the Admin GUI is easiest. OK, so you have your volunme, how does your instance see it? It’s not too obvious from their documentation but in CentOS my extra volume is


I mounted that a formatted it as an ext4 device as per their instructions. It didn’t take that long. I put in a line in /etc/fstab like this:

/dev/xvdj /mnt/vol ext4 defaults 1 2

Now I’m good to go! It gets mounted after reboot.

Dec, 2016 update
Amazon has announced Lightsail to better compete with GoDaddy and their ilk. Plans start as low as $5 a month. For $10 a month you get a static IP, 1 GB RAM, 20 GB SSD storage I think and ssh access. So I hope that means root access. Oh, plus a pre-configured WordPress software.

Amazon EC2 rocks. They could have charged a premium but instead they are the cheapest offering out there according to my informal survey. The richness of their service offerings is awesome. I didn’t mention that you can mount the entire data set of the human genome, or all the facts of the world which have been assembled in How cool is that?