What

• Writing better applications
• Tuning your servers and hosting
• Improving user networks

Me

• Apprentice since Autumn 2020 at a Linux Distributor
• Likes server hosting things, storage, networked thingies
• Reads RFCs, IETFs, kernel code and documentation
• Does system level C, Python, Bash and a little Ruby

• Likes to present other people’s work

This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

Writing better applications

Round Trip Time

An HTTPS 1.1 TLS1.2 Request

Let’s count

• 30ms times 8 RTTs = 240ms
• 150ms times 8 RTTs = 1200ms
• 240ms times 50 Requests = 12.000s
• 1200ms times 50 Requests = 60.000s

Reuse the connection!

Reuse connections in the Web!

• Connect to webserver and download HTML
• Parse the HTML
• Our CSS is in another castle
• Connect to other webserver and download CSS
• Parse stylesheet
• Start rendering page

Don’t:

Do:

• JS and CSS library CDNs are not pratically better
• If you need a CDN, use a CDN
• Cross Site Resource caching is dead
• External embedded images or videos are fine

Tuning your servers

Good old TCP

• connection oriented
• detects errors and asks for retransmissions
• guarantees send order
• has you acknowledge packets
• employs network congestion avoidance

Congestion Control

• Default on Linux: cubic

• Default on FreeBSD: newreno

• Default for Torrents: ledbat

BBR

• Delay based congestion detection not just lost based congestion detection
• More aggresive probing

https://blog.cloudflare.com/http-2-prioritization-with-nginx/

/etc/sysctl.d/custom.conf

net.ipv4.tcp_congestion_control=bbr
net.ipv4.tcp_notsent_lowat=16384
net.core.default_qdisc=fq

https://grapheneos.org/articles/server-traffic-shaping

Use a newer HTTP version

Apache:

<VirtualHost ...>
    Protocols h2 h2c http/1.1
</VirtualHost>

Nginx:

server {
    listen 443 ssl http2;
}

Improving user networks

Want some cake?

Data path

• Bufferbloat is when your hops buffer too much
• Buffers too small -> low throughput
• Buffers too big -> high latency

• Latency without load != Latency under load

• Latency rises if slowest link is highly utilised
• -> Should notify about congestion to avoid peak utilisation
• –> Drop Packets or add a controlled delay

Cake Gains:

• Consistent Latency
• Simultaneous Low Latency Voice Calls and Steam Downloads
• Fast web and apps

Cake Caveats:

• Requires static knowledge of maximum link speed (-> not suitable for mobile)
• Usually 5-10% throughput loss
• Breaks NAT offloading

Thanks!

Presentation available at:

https://0x90.space/tamara-iger-talk/

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