Skip to content

Instantly share code, notes, and snippets.

@azet
azet / Datacenter-Operations__here_be_dragons.md
Last active May 29, 2025 15:15
Reading material for Operations & Datacenter engineers and managers

Check Out these projects, papers and blog posts if you're working on Geo redundant Datacenters or even if you only need to have your software hosted there. It's good to know what you're in for.

  Collected these for a colleague, these have been super useful over 
  the past 15+ years and and will most likely help and/or entertain you. 
  May be extended in the future.
  -- azet (@azet.org)

load balancing

DNS geo & anycast

@zingaburga
zingaburga / sve2.md
Last active May 17, 2025 21:36
ARM’s Scalable Vector Extensions: A Critical Look at SVE2 For Integer Workloads

ARM’s Scalable Vector Extensions: A Critical Look at SVE2 For Integer Workloads

Scalable Vector Extensions (SVE) is ARM’s latest SIMD extension to their instruction set, which was announced back in 2016. A follow-up SVE2 extension was announced in 2019, designed to incorporate all functionality from ARM’s current primary SIMD extension, NEON (aka ASIMD).

Despite being announced 5 years ago, there is currently no generally available CPU which supports any form of SVE (which excludes the [Fugaku supercomputer](https://www.fujitsu.com/global/about/innovation/

tl;dr:

  • mostly, hosts ignore the mss sent
  • most of the interesting behaviour comes from the extremes: mss=1 and mss=1440
  • setting mss=(an atypical value, say 1275 or 1411) ought to spot hosts that simply reflect MSS values
  • setting mss=1024 apparently will spot a bunch of (Microsoft?) hosts returning MSS=956
  • passively, mss=1220, 1360, 1410 may help identify CDN/non-CDN nodes inside yahoo/edgecast, google, facebook respectively

Longer version: captured SYN+ACK+MSS values:

Variation is less than I initially thought; just enough for me to notice

# +---------+
# | |
# | RT1 |
# | 1.1.1.1 |-lo1 (2001:db8:1000::1/128)
# | |
# +---------+
# |rt1-eth0 (.1)
# |
# |10.0.1.0/24
# |2001:DB8:1::/64
ripd# conf t
ripd(config)# router rip
ripd(config-router)# network eth2
ripd(config-router)# show configuration candidate changes
@@ -14,6 +14,7 @@
distance 25 172.16.1.0/24
network eth0
network eth1
+ network eth2
redistribute ospf metric 3
@mutin-sa
mutin-sa / Top_Public_Time_Servers.md
Last active June 1, 2025 22:41
List of Top Public Time Servers

Google Public NTP [AS15169]:

time.google.com

time1.google.com

time2.google.com

time3.google.com

# +---------+ +---------+
# | | | |
# | CE1 | | CE2 |
# | | | |
# +---------+ +---------+
# ce1-eth0| |ce2-eth0
# | |
# 172.16.1.0/24| |172.16.2.0/24
# | |
# rt1-eth0| 10.0.1.0/24 10.0.3.0/24 |rt3-eth0
@skreuzer
skreuzer / prometheus.yml
Last active February 7, 2019 18:45
smokeping style metrics in prometheus
global:
evaluation_interval: 15s
rule_files:
- smokeping.rules
scrape_configs:
- job_name: 'blackbox_icmp'
metrics_path: /probe
params:
module: [icmp]
scrape_interval: 1s
@grkvlt
grkvlt / honest-achmed.txt
Created July 7, 2017 18:27
Honest Achmed's Used Cars and Certificates
This is a request to add the CA root certificate for Honest Achmed's Used Cars and Certificates. The requested information as per the CA information checklist is as follows:
1. Name
Honest Achmed's Used Cars and Certificates
2. Website URL
www.honestachmed.dyndns.org
@marcan
marcan / linux.sh
Last active July 21, 2024 14:00
Linux kernel initialization, translated to bash
#!/boot/bzImage
# Linux kernel userspace initialization code, translated to bash
# (Minus floppy disk handling, because seriously, it's 2017.)
# Not 100% accurate, but gives you a good idea of how kernel init works
# GPLv2, Copyright 2017 Hector Martin <[email protected]>
# Based on Linux 4.10-rc2.
# Note: pretend chroot is a builtin and affects the current process
# Note: kernel actually uses major/minor device numbers instead of device name