Simon MottAll about me
Simon Mott - All about me
Simon Mott

Yearly Archives

6 Articles

Routed Subnets, rp_filter and arp_ignore

by Simon

Over the past couple of years, I’ve been quite accustomed to my ISP providing me with an IP block (typically a /29) instead of just a single static IP, but recently I’ve switched to Hyperoptic for their FTTP offering (Because, Gigabit!). Unfortunately, they seem to only offer single IPs for residential service and require you to be on their business package which costs £££ if you want more IPs.

To get around this I decided to try to tunnel some IPs home – My setup is rather complex but I’m going to skip over the specifics for most of it and focus on the issue I was facing – lets ignore how the IPs route around the rest of my network and ultimately end up at the router for now and just look at the rather simplified view below.

Odd behaviour with /etc/mtab being a regular file

by Simon

One of our customers had recently requested a Bare-Metal Restore (BMR) of one of their servers; which is a pretty routine task for us. However, upon bringing the restored server up I’d noticed some odd behaviour with some of its services, notably snmpd.

Our monitoring successfully polls most metrics that we look for, however fails on getting disk statistics and eventually snmpd just starts timing out. Using snmpbulkwalk I could see that I was getting a response right up until midway through the HOST-RESOURCES MIB. It did look to be hanging on mount points and once snmpbulkwalk had timed out, I couldn’t get a successful response from snmpd again. This was also seemingly affecting MariaDB, preventing it from starting, amongst other things.

Growing my Linux RAID5 array

by Simon

Recently I’ve needed to expand my RAID5 array by adding another disk. My experience with mdadm since starting to use it back in 2009 was for RAID1 only so I’ve never really needed to actually expand an array and so I thought I’d document the process here for future reference.

This process should in theory work for RAID4 and RAID6 personailities too, not just RAID5.

My array consists of 4x 3TB WD Red NAS drives in RAID5 for a total of ~9TB of space. I’m not going to cover creating of the array here because its mostly the same as RAID1, this instead will cover how to add a new disk to it and subsequent growing of LVM and ext4 to make use of the extra space. You can see how everything is stacked together in the image below.

Slow DNS resolving using bind9 as caching resolver

by Simon

I currently have 4 DNS servers across my estate and until recently these were all configured to forward all queries to Google DNS (8.8.8.8). I ended up having an issue with Google caching an undesired record value so I opted to change my DNS servers so that they no longer forward queries elsewhere, but instead try to answer it themselves; Doing this gives me slightly more control over my DNS cache.

As I use named (bind9) this was a pretty trivial change – Simply remove the forwarders { 8.8.8.8; }; clause in my configuration and that should be that.

During my post-change testing though I’d noticed that resolution was taking significantly longer for un-cached queries than I’d expect (microsoft.gointeract.io is only used to illustrate my issue):

PHP Handlers and PHP 5 vs 7

by Simon

php_logoThe idea for this post actually came from observing performance after moving this site over to WordPress (and to a lesser extent, my other website, General Photography). I use Puppet orchestration for my servers and I made the mistake of trying to convert everything to puppet manifests and also get things working how I wanted without fully understanding how puppet works at the same time; That however is another story. This does means that my puppet manifests are not very flexible currently and I use suphp as my main PHP handler just because for me, at the time, it was easier.

That being said – I’m fully aware of the performance issues suphp exhibits because my Observium install used it at first – it now uses mod_php because loading all the graphs was noticably slow. I thought I’d try to quantify the performance differences between suphp and mod_php and decided I should do all 3 common PHP handlers. Whilst I was gathering metrics for this I decided It’d be useful to include PHP7 results too.

Caching with Apache’s mod_cache and mod_deflate

by Simon

I currently work in the hosting industry and as part of my job I have to deal with WordPress on a regular basis and as such I’ve seen how appalling it can be sometimes with regards to page loading times. Given that my content on here doesn’t change all too often, it makes sense to spend the time generating the content only once and serving it to meet multiple requests for the same document. In order to do this one would usually employ some form of caching.

WordPress itself does have the option for multiple caching plugins which integrate nicely but in my experience they still have to pass the request off to a PHP handler which means some processing is still needed to accommodate the request (albeit less than a full page load). For the purposes of this article though, I’m going to assume a generic framework as this technique is not specific to WordPress at all.

There’re a number of software solutions to sit in front of your web server which act as a cache and some of the more notable ones are nginx and varnish and each have their pros and cons (As far as I know, Varnish can’t do native SSL termination yet). For this post though, I’ll be making use of some Apache modules to do the same thing. This was mostly an experiment for myself to see what I could do with it – I’ve found some limitations which as of yet I haven’t been able to work around for lack of knowledge on the inner workings of Apache, but for now It does the job.