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README example for using checkpoint/restore. 

Docker-DCO-1.1-Signed-off-by: Ross Boucher <rboucher@gmail.com> (github: boucher)
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boucher 2015-05-20 17:59:19 -07:00
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## libcontainer - reference implementation for containers [![Build Status](https://jenkins.dockerproject.com/buildStatus/icon?job=Libcontainer Master)](https://jenkins.dockerproject.com/job/Libcontainer%20Master/) ## libcontainer - reference implementation for containers [![Build Status](https://jenkins.dockerproject.com/buildStatus/icon?job=Libcontainer Master)](https://jenkins.dockerproject.com/job/Libcontainer%20Master/)
Libcontainer provides a native Go implementation for creating containers Libcontainer provides a native Go implementation for creating containers
with namespaces, cgroups, capabilities, and filesystem access controls. with namespaces, cgroups, capabilities, and filesystem access controls.
It allows you to manage the lifecycle of the container performing additional operations It allows you to manage the lifecycle of the container performing additional operations
after the container is created. after the container is created.
#### Container #### Container
A container is a self contained execution environment that shares the kernel of the A container is a self contained execution environment that shares the kernel of the
host system and which is (optionally) isolated from other containers in the system. host system and which is (optionally) isolated from other containers in the system.
#### Using libcontainer #### Using libcontainer
@ -27,7 +27,7 @@ if err != nil {
} }
``` ```
Once you have an instance of the factory created we can create a configuration Once you have an instance of the factory created we can create a configuration
struct describing how the container is to be created. A sample would look similar to this: struct describing how the container is to be created. A sample would look similar to this:
```go ```go
@ -120,9 +120,9 @@ Additional ways to interact with a running container are:
```go ```go
// return all the pids for all processes running inside the container. // return all the pids for all processes running inside the container.
processes, err := container.Processes() processes, err := container.Processes()
// get detailed cpu, memory, io, and network statistics for the container and // get detailed cpu, memory, io, and network statistics for the container and
// it's processes. // it's processes.
stats, err := container.Stats() stats, err := container.Stats()
@ -137,18 +137,18 @@ container.Resume()
#### nsinit #### nsinit
`nsinit` is a cli application which demonstrates the use of libcontainer. `nsinit` is a cli application which demonstrates the use of libcontainer.
It is able to spawn new containers or join existing containers. A root It is able to spawn new containers or join existing containers. A root
filesystem must be provided for use along with a container configuration file. filesystem must be provided for use along with a container configuration file.
To build `nsinit`, run `make binary`. It will save the binary into To build `nsinit`, run `make binary`. It will save the binary into
`bundles/nsinit`. `bundles/nsinit`.
To use `nsinit`, cd into a Linux rootfs and copy a `container.json` file into To use `nsinit`, cd into a Linux rootfs and copy a `container.json` file into
the directory with your specified configuration. Environment, networking, the directory with your specified configuration. Environment, networking,
and different capabilities for the container are specified in this file. and different capabilities for the container are specified in this file.
The configuration is used for each process executed inside the container. The configuration is used for each process executed inside the container.
See the `sample_configs` folder for examples of what the container configuration should look like. See the `sample_configs` folder for examples of what the container configuration should look like.
To execute `/bin/bash` in the current directory as a container just run the following **as root**: To execute `/bin/bash` in the current directory as a container just run the following **as root**:
@ -156,18 +156,50 @@ To execute `/bin/bash` in the current directory as a container just run the foll
nsinit exec --tty /bin/bash nsinit exec --tty /bin/bash
``` ```
If you wish to spawn another process inside the container while your If you wish to spawn another process inside the container while your
current bash session is running, run the same command again to current bash session is running, run the same command again to
get another bash shell (or change the command). If the original get another bash shell (or change the command). If the original
process (PID 1) dies, all other processes spawned inside the container process (PID 1) dies, all other processes spawned inside the container
will be killed and the namespace will be removed. will be killed and the namespace will be removed.
You can identify if a process is running in a container by You can identify if a process is running in a container by
looking to see if `state.json` is in the root of the directory. looking to see if `state.json` is in the root of the directory.
You may also specify an alternate root place where You may also specify an alternate root place where
the `container.json` file is read and where the `state.json` file will be saved. the `container.json` file is read and where the `state.json` file will be saved.
#### Checkpoint & Restore
libcontainer now integrates [CRIU](http://criu.org/) for checkpointing and restoring containers.
This let's you save the state of a process running inside a container to disk, and then restore
that state into a new process, on the same machine or on another machine.
`criu` version 1.5.2 or higher is required to use checkpoint and restore.
If you don't already have `criu` installed, you can build it from source, following the
[online instructions](http://criu.org/Installation). `criu` is also installed in the docker image
generated when building libcontainer with docker.
To try an example with `nsinit`, open two terminals to the same busybox directory.
In the first terminal, run a command like this one:
```bash
nsinit exec -- sh -c 'i=0; while true; do echo $i; i=$(expr $i + 1); sleep 1; done'
```
You should see logs printing to the terminal every second. Now, in the second terminal, run:
```bash
nsinit checkpoint --image-path=/tmp/criu
```
The logs in your first terminal will stop and the process will exit. Finally, in the second
terminal, run the restore command:
```bash
nsinit restore --image-path=/tmp/criu
```
The process will resume counting where it left off and printing to the new terminal window.
#### Future #### Future
See the [roadmap](ROADMAP.md). See the [roadmap](ROADMAP.md).