I recently encountered a behaviour in Nginx that I didn’t expect and caused a production outage in the process. While I would love to blame DNS for this, as it’s usually the cause of most network-related issues, in this case, the fault lies with Nginx. I was running a very simple Nginx proxy, relaying an internal service to the outside world. The internal service is behind an AWS ALB, and the Nginx configuration was proxying to the ALB’s FQDN:...
I noticed when running an Alpine based virtual machine with Consul DNS forwarding set up, that sometimes the machine couldn’t resolve *.consul domains, but not in a consistent manner. Inspecting the logs looked like the request was being made and responded to successfully, but the result was being ignored. After a lot of googling and frustration, I was able to track down that it’s down to a difference (or optimisation) in musl libc, which glibc doesn’t do....
I use Vagrant when testing new machines and experimenting locally with clusters, and since moving (mostly) to Linux, I have been using the LibVirt Plugin to create the virtual machines. Not only is it significantly faster than Hyper-V was on windows, but it also means I don’t need to use Oracle products, so it’s win-win really. The only configuration challenge I have had with it is setting up VM hostname resolution, and as I forget how to do it each time, I figured I should write about it....
I was recently using my Hashibox for a test, and I noticed the DNS resolution didn’t seem to work. This was a bit worrying, as I have written about how to do DNS resolution with Consul forwarding in Ubuntu, and apparently something is wrong with how I do it. Interestingly, the Alpine version works fine, so it appears there is something not quite working with how I am configuring Systemd-resolved....
DEPRECATED - This has a race condition! Please see this post for an updated version which works! Following on from the post the other day on setting up DNS forwarding to Consul with SystemD, I wanted also to show how to get Consul up and running under Alpine Linux, as it’s a little more awkward in some respects. To start with, I am going to setup Consul as a service - I didn’t do this in the Ubuntu version, as there are plenty of useful articles about that already, but that is not the case with Alpine....
DEPRECATED - This doesn’t work properly Please see this post for an updated version which works! One of the advantages of using Consul for service discovery is that besides an HTTP API, you can also query it by DNS. The DNS server is listening on port 8600 by default, and you can query both A records or SRV records from it. SRV records are useful as they contain additional properties (priority, weight and port), and you can get multiple records back from a single query, letting you do load balancing client side:...