difference between cgroups and namespaces

The proper links for those two notions have been fixed in PR 14307:

Under the hood, Docker is built on the following components:

The cgroups and namespaces capabilities of the Linux kernel

With:

• cgroup: Control Groups provide a mechanism for aggregating/partitioning sets of tasks, and all their future children, into hierarchical groups with specialized behaviour.
• namespace: wraps a global system resource in an abstraction that makes it appear to the processes within the namespace that they have their own isolated instance of the global resource.

In short:

• Cgroups = limits how much you can use;
• namespaces = limits what you can see (and therefore use)

See more at "Anatomy of a Container: Namespaces, cgroups & Some Filesystem Magic" by Jérôme Petazzoni.

Cgroups involve resource metering and limiting:

• memory
• CPU
• block I/O
• network

Namespaces provide processes with their own view of the system

Multiple namespaces:

• pid
• net
• mnt
• uts
• ipc
• user: userns it is graduating from experimental in docker 1.10
  (per-daemon-instance remapping of container root to an unprivileged user is in progress: PR 12648: see its design)

cgroups limits the resources which a process or set of processes can use these resources could be CPU,Memory,Network I/O or access to filesystem while namespace restrict the visibility of group of processes to the rest of the system.

visit for further details How Linux Kernel Cgroups And Namespaces Made Modern Containers Possible

Cgroups(control groups) does resource management.
It determines how much host machine resources to be given to containers.

for example:-we define resources in docker-compose yaml file for creating services like:

resources:  limits:    cpus: "0.1" (100 millicores)    memory: 50M

Here, in this example we are explicitly asking cgroups to allocate these resources to particular container.

Namespaces: provides process isolation, complete isolation of containers, separate file system.