As always with her blog posts, this one is very focused on one particular subject, easy to read, and explains things simply, so that the reader’s technical level is always irrelevant (OK, OK, you do need a basic understanding of how HTTP works, but not more than that).
Here are a couple of useful Bash resources that came upon my radar recently.
First one is Julia Evans’ blog post “Bash scripting quirks & safety tips“. It’s quite introductory, but is has a few useful tips. The one in particular I
either didn’t know about or completely forgot mentioned recently is on how to make Bash scripts safer by using “set -e“, “set -u“, and “set -o pipefail“. These go well with another post of mine not so long ago.
The second is Sam Rowe’s blog post “Advancing in the Bash Shell“, which I found useful for all kinds of navigation and variable expansion in Bash command line. Especially the bits on searching and reusing the history.
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 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.
Picking the right settings for your SSL certificates and SSL configuration on your webserver is confusing. As far as I understand it there are about 3 billion settings. Here is an example of an SSL Labs result for mail.google.com. There is all this stuff like
OLD_TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256on that page (for real, that is a real thing.). I’m happy there are tools like SSL Labs that help mortals make sense of all of it.