Sysadmin

How to handle configuration in PHP

Kevin Schroeder has a blog post about the tool that he is building for configuration management in PHP. The library is still in the early pre-release stage, but it looks like it solves quite a few problems related to configuration, like nesting, inheritance, and environment/context variation.

Here’s the YouTube video that provides a bit of introduction into how to use the tool, and what to expect of it.

The only thing that dials down my excitement in this implementation is the use of XML, even though I understand why he opted for this choice.

I will need a PHP configuration management solution soon, but the priority hasn’t been raised high enough yet for me to jump into the research. If you know of any other similar tools, please let me know – it all will come handy pretty soon.

MySQL 8 is coming

OpenSource.com covers the upcoming release of the MySQL 8.

What happened to 6 & 7?

Years ago, before the Sun Microsystems purchase of MySQL AB, there was a version of MySQL with the number 6. Sadly, it was a bit ambitious and the change of ownership left it to wither. The MySQL Cluster product has been using the 7 series for years. With the new changes for MySQL 8, developers feel they have modified it enough to bump the big number.

The new version brings a whole lot of changes to filesystem organization, indexes, faster ALTER TABLE, and more.

Fixing outdated Let’s Encrypt (zope.interface error)

I’ve started using Let’s Encrypt for the SSL certificates a while back. I installed it on all the web servers, irrelevant of the need for SSL, just to have it there, when I need it (thanks to this Ansible role). One of those old web servers needed an SSL certificate recently, so I thought it’d be no problem to generate one.

But I was wrong. The letsencrypt-auto tool got outdated and was failing to execute, throwing some Python exception about missing zope.interface module. A quick Google search brought this StackOverflow discussion, with the exact issue I was having.

Traceback (most recent call last):
  File "/root/.local/share/letsencrypt/bin/letsencrypt", line 7, in <module>
    from certbot.main import main
  File "/root/.local/share/letsencrypt/local/lib/python2.7/dist-packages/certbot/main.py", line 12, in <module>
    import zope.component
  File "/root/.local/share/letsencrypt/local/lib/python2.7/dist-packages/zope/component/__init__.py", line 16, in <module>
    from zope.interface import Interface
ImportError: No module named interface

However, the solution didn’t fix the problem for me:

unset PYTHON_INSTALL_LAYOUT
/opt/letsencrypt/letsencrypt-auto -v

Even pulling the updated version from the GitHub repository didn’t solve it.

After poking around for a while more, I found this bug report from the last year, which solved my problem.

I recommend:

Running rm -rf /root/.local/share/letsencrypt. This removes your installation of letsencrypt, but keeps all configuration files, certificates, logs, etc.

Make sure you have an up to date copy of letsencrypt-auto. It can be found here.

Run letsencrypt-auto again.

If you get the same behavior, you can try installing zope.interface manually by running:

/root/.local/share/letsencrypt/bin/pip install zope.interface

Hopefully, next time I’ll remember to search my blog’s archives …

Update (May 31, 2017): check out my brother’s follow up post with even better way of fixing this issue.

Mcrouter: a memcached protocol router

Mcrouter is an Open Source tool developed by Facebook for scaling up the memcached deployments:

Mcrouter is a memcached protocol router for scaling memcached (http://memcached.org/) deployments. It’s a core component of cache infrastructure at Facebook and Instagram where mcrouter handles almost 5 billion requests per second at peak.

Here is a good overview of some of the scenarios where Mcrouter is useful. There’s more than one. Here are some of the features to get you started:

Memcached ASCII protocol
Connection pooling
Multiple hashing schemes
Prefix routing
Replicated pools
Production traffic shadowing
Online reconfiguration
Flexible routing
Destination health monitoring/automatic failover
Cold cache warm up
Broadcast operations
Reliable delete stream
Multi-cluster support
Rich stats and debug commands
Quality of service
Large values
Multi-level caches
IPv6 support
SSL support

Amazon AWS : MTU for EC2

I came across this handy Amazon AWS manual for the maximum transfer unit (MTU) configuration for EC2 instances. This is not something one needs every day, but, I’m sure, when I need it, I’ll otherwise be spending hours trying to find it.

The maximum transmission unit (MTU) of a network connection is the size, in bytes, of the largest permissible packet that can be passed over the connection. The larger the MTU of a connection, the more data that can be passed in a single packet. Ethernet packets consist of the frame, or the actual data you are sending, and the network overhead information that surrounds it.

Ethernet frames can come in different formats, and the most common format is the standard Ethernet v2 frame format. It supports 1500 MTU, which is the largest Ethernet packet size supported over most of the Internet. The maximum supported MTU for an instance depends on its instance type. All Amazon EC2 instance types support 1500 MTU, and many current instance sizes support 9001 MTU, or jumbo frames.

The document goes into the detail of how to set, check and troubleshoot MTU on the EC2 instances, which instance types support jumbo frames, when you should and shouldn’t change the MTU, etc.

The following instances support jumbo frames:

Compute optimized: C3, C4, CC2

General purpose: M3, M4, T2

Accelerated computing: CG1, G2, P2

Memory optimized: CR1, R3, R4, X1

Storage optimized: D2, HI1, HS1, I2

As always, Julia Evans has got you covered on the basics of networking and the MTU.