Linux Container Basics Michael Kehoe Staff Site Reliability Engineer 

Michael Kehoe $ WHOAMI • Staff Site Reliability Engineer @ LinkedIn • Production-SRE Team; • Disaster Recovery • Incident Response • Visibility Engineering • Reliability Principles • Find me online at: • @matrixtek • https://michael-kehoe.io • linkedin.com/in/michaelkkehoe 

Outline 1 What are Containers 2 Containers, Zones, Jails, VMs 3 Containers in detail 4 Containers: cgroups 5 Containers: Namespaces 6 Containers: CoW 7 Containers: LSM 8 Runtimes 

What are containers? 

“CONTAINERS ARE NOT A REAL THING!!!” J E S S I E F R A Z E L L E https://twitter.com/thejsj/status/840295431779172352 

Wait, What??? 

“The word ‘container’ doesn’t mean anything super precise. Basically there are a few new Linux kernel features (‘namespaces’ and ’cgroups’) that let you isolate processes from each other. When you use those features, you call it ‘containers’” J U L I A E V A N S https://jvns.ca/blog/2016/10/10/what-even-is-a-container/ 

“Containers are processes, born from tarballs, anchored to namespaces, controlled by cgroups” A L I C E G O L D F U S S https://twitter.com/lucacanducci/status/1011909897640927232 

Containers • Security Wise: Acts like a chroot jail • Resource Wise: Similar to VM • Deployment Wise: Fast and lightweight What are containers? 

Containers, Zones, Jails, VMs 

Built off chroot BSD Jails • Processes created in the chrooted environment cannot access files or resources outside of it* • Processes are only limited by the part of the filesystem they can access • Four key elements: • Directory subtree • Hostname • IP Address • Command to run BSD Jails 

Virtualizing operating system services Solaris Zones • A zone is a virtualized operating system environment created within a single instance of the Solaris Operating System • Root zone – Default zone for the system & system-wide administrative tasks • Non-global zone - Zones for running specific workloads Solaris Zones 

Solaris Zones https://docs.oracle.com/cd/E19044-01/sol.containers/817-1592/zones.intro-1/index.html 

Solaris Zones FEATURES Processes cannot change zones Security Zone can provide isolation at almost any level of granularity Granularity Applications are prevented from monitoring or intercepting each other's network traffic, file system data, or process activity. Isolation Flexible network segmentation options Network Isolation The same application environment can be maintained on different physical machines Virtualization https://docs.oracle.com/cd/E19044-01/sol.containers/817-1592/zones.intro-1/index.html 

Emulation of a Computer System Virtual Machine • Hypervisor uses native execution to share & manage hardware • Multiple environments isolated from each other • Separate kernel & operating system instances Virtual Machine 

Containers Limiting the resources that can be used by a process/ set of processes cgroups Isolating filesystem resources Namespaces Implicit sharing or shadowing Copy on Write Locking down container privileges Linux Security Modules 

Containers in detail: cgroups 

cgroups • CPU – Limit CPU bandwidth • Cpuacct • Cpuset • Memory – Control the userland memory, kernel data structures, TCP socket buffers • IO – Control bandwidth or IOPS • PID-Limit number of PIDs • Network – Control Bandwidth * • And more… * With use of tc/ iptables Containers in Detail 

Containers in detail: Namespaces 

Namespaces • CGroup – Cgroup root directory • IPC – Control the userland memory, kernel data structures, TCP socket buffers • Network (net) – Network devices/ stacks/ ports • Mount – Mount points can be private or shared • Process ID (pid) – Only see PID’s in same PID namespace • User ID (user) – Mapping of UID’s • UTS – Set the hostname in cgroup Containers in Detail 

Containers in detail: CoW 

Copy on Write • Reduces memory footprint • Helps to reduce container boot times • Details: • Memory “resource” can be shared if only read • Copy of data is deferred until first write Containers in Detail 

Containers in detail: LSM 

Linux Security Modules • AppArmor • SELinux • Seccomp • Capabilities • NoNewPrivs Containers in Detail 

Container Runtimes 

Container Runtimes • LXC • runc • lmctfy • cri-o • containerd • rkt Container Runtimes 

Other Resources ZONES Oracle: System Administration Guide: Oracle Solaris Containers-Resource Management and Oracle Solaris Zones https://docs.oracle.com/cd/E19044-01/sol.containers/817-1592/zones.intro-1/index.html https://docs.oracle.com/cd/E19253-01/817-1592/zone/index.html Brendan Gregg: Documentation: Zones http://www.brendangregg.com/zones.html#resource0 

Other Resources CONTAINERS Jerome Petazzoni: Anatomy of a Container: Namespaces, cgroups & Some Filesystem Magic - LinuxCon https://www.slideshare.net/jpetazzo/anatomy-of-a-container-namespaces-cgroups-some-filesystem-magic- linuxcon Jessie Frazelle: Containers from User Space (LinuxConfAU 2018) https://docs.google.com/presentation/d/1UuHvR_kvZ3BF1pSXyv4mMKX9vmGr7GXm97USx7mzTXY/ Julia Evans: What is even a container https://jvns.ca/blog/2016/10/10/what-even-is-a-container/ Redhat: Managing system resources on Red Hat Enterprise Linux 6 & 7 https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/6/html- single/resource_management_guide/index https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html- single/resource_management_guide/index Akihiro Suzuki: Real-Time Task Partitioning using Cgroups https://elinux.org/images/8/84/Real-Time_Tasks_Partitioning_using_Cgroups.pdf 

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