Everything has limits, including software systems. When you hit these limits, bad things can happen.
You've probably hit memory and disk limits, but those aren't the only ones.
This page lists limits that, when breached, led to someone having a bad time. I tweeted about limits and got all sorts of interesting responses. This page contains some of them, with links to the tweets, which often contain more details.
inodes. @aegis, Alex Elman, Benjamin Stein, Thomas Attree, @dmolnar, @anotherwalther, Jinsy Oommen, Rafael Jesus, Ondrej Kokes, Peter Wang, Cadey A. Ratio, @williamsjoe, Nic Wise, ericdennis
open file descriptors / handles. Moritz Lenz, Matt McDonald, @aegis, Bruno Félix, Ken Carroll, @ehashdn, Jeff Bean, @patriotvn, Peter Wang, @asm0dio, @williamsjoe, ericdennis, Jakub Korab
processes (pids). @RuinTaughtMe, @patriotvn, Matt Tex Ackerle, @pete23com
Ports. @qudooschaudhry, Alex Hidalgo, Rafael Jesus, @williamsjoe
TCP connections. Sheeri K. Cabral, @Pluto_Berlin
Threads. @dbsmasher, David Bezley
Entropy pool. Justin Manchester, Petru Ratiu
Shebang length. @bengerman13, Anthony Sottile
Virtual memory. @shanemhansen, @williamsjoe
How fast the kernel can find an unused port to allocate a new connection. Sean Kilgore
Pod memory limits. @dastbe
Environment variable size. Glen Mailer
Java ring buffer size. Richard Tibbetts
.NET framework threadpool I/O completion port limit. Brandon Paddock
SQL Server buffer cache. Dave Poole
Concurrency limit of Java concurrent hash map. Matt McDonald
ulimit on number of processes that can be run per user. Ben Hemphill
memlock with JVM. @aegis
IOPs Arie Kachler, Jesse Noller
System time divergence. Nicolai von Neudeck
Goroutines. @beccadottex
Number of fields in an elastic search index. @bengerman13
Filename / path size limit, on Windows. @BennettElder, Peter Wang
Number of vlans in vmware vcloud director, 2015 edition. Jose manuel de arce
ipconntrack. @shanemhansen, Glen Mailer
Load balancer license connection limits. Franklin Wirtz
Wal senders. Max Knee
Kernel udp rx buffer size. @sjoeboo
Network bandwidth. @anotherwalther, Rafael Jesus
AWS API limit on number of requests made per minute when requesting new instances. Justin Manchester
Number of links to a file. @mendel
Number of files per directory. @hlieberman
VPC DNS packet limits. Rafael Jesus
Number of huge pages. @patriotvn
Connections to Oracle database. Viktor Gamov
Socket filename length limit. Anthony Sottile
Stack size. @williamsjoe
Buffer exhaustion in NICs & switches. @williamsjoe
AWS EC2 instance count limits. Nic Wise
Time Wait Assasination. John Allspaw
Semaphores. @rknayyar
Number of OS threads. AWS 2020-11-25