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Operating System

"Software that manages software"

"Scheduler"

• Coordinates with CPU
• Manages "context switching"
• Swap out Program Counter

Operating system

Multiple cores?

Multiple threads?

Multiple Program Counters!

"Process"

Processes

• Know about each other
• Communicate with each other
• Get the same system info from OS
• Spawn new processes
• Exist in a hierarchy

Virtual memory

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*

Namespaces

• Linux can tell different lies
• Bundle processes together
• Different lie for each bundle

Mount Namespace

Network namespace

User namespace

• Namespace-local user
• Map local user to global user
• ... even root

User namespace

A process can be local-root!

Control Group hierarchy

• Separate from process hierarchy
• Nodes with "controllers"
• Tracking, auditing, capping

Control Groups

Set of processes that...

• Know of only each other
• Have a root user
• Have their own file tree
• Have their own network config
• Have their own hostname
• Have no way out of that box
• Have a restricted finite set of resources

Let's call it a "Container"

Orchestration

Read-only containers

• Load once, run multiple
• No write collisions
• Trivial overhead

Run anywhere?

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Static compiler for your entire system

Few processes

$ ps axf
 PID TTY      STAT   TIME COMMAND
   1 ?        Ss     0:06 init [2]
  72 ?        Ss     0:06 runsvdir -P /etc/service log: .................................................................
  78 ?        Ss     0:00  \_ runsv ssh
 105 ?        S      0:00  |   \_ /usr/sbin/sshd -D
2516 ?        Ss     0:00  |       \_ sshd: web [priv]
2518 ?        S      0:00  |           \_ sshd: web@pts/0
2519 pts/0    Ss     0:00  |               \_ -bash
2605 pts/0    R+     0:00  |                   \_ ps axf
  79 ?        Ss     0:00  \_ runsv nginx
  99 ?        S      0:00  |   \_ nginx: master process /usr/sbin/nginx -g daemon off; error_log /var/log/error.log; -c /
 104 ?        S      0:00  |       \_ nginx: worker process
  80 ?        Ss     0:00  \_ runsv newrelic
  81 ?        Ss     0:00  \_ runsv app
  89 ?        Ss     0:22      \_ php-fpm: master process (/etc/php/7.2-zts/fpm/php-fpm.conf)

Cluster is the unit of deployment

Docker layered filesystem

Different uses, different trade-offs

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