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diff --git a/g3doc/README.md b/g3doc/README.md deleted file mode 100644 index 7956fe739..000000000 --- a/g3doc/README.md +++ /dev/null @@ -1,168 +0,0 @@ -# What is gVisor? - -gVisor is an application kernel, written in Go, that implements a substantial -portion of the [Linux system call interface][linux]. It provides an additional -layer of isolation between running applications and the host operating system. - -gVisor includes an [Open Container Initiative (OCI)][oci] runtime called `runsc` -that makes it easy to work with existing container tooling. The `runsc` runtime -integrates with Docker and Kubernetes, making it simple to run sandboxed -containers. - -gVisor can be used with Docker, Kubernetes, or directly using `runsc`. Use the -links below to see detailed instructions for each of them: - -* [Docker](./user_guide/quick_start/docker.md): The quickest and easiest way - to get started. -* [Kubernetes](./user_guide/quick_start/kubernetes.md): Isolate Pods in your - K8s cluster with gVisor. -* [OCI Quick Start](./user_guide/quick_start/oci.md): Expert mode. Customize - gVisor for your environment. - -## What does gVisor do? - -gVisor provides a virtualized environment in order to sandbox containers. The -system interfaces normally implemented by the host kernel are moved into a -distinct, per-sandbox application kernel in order to minimize the risk of an -container escape exploit. gVisor does not introduce large fixed overheads -however, and still retains a process-like model with respect to resource -utilization. - -## How is this different? - -Two other approaches are commonly taken to provide stronger isolation than -native containers. - -**Machine-level virtualization**, such as [KVM][kvm] and [Xen][xen], exposes -virtualized hardware to a guest kernel via a Virtual Machine Monitor (VMM). This -virtualized hardware is generally enlightened (paravirtualized) and additional -mechanisms can be used to improve the visibility between the guest and host -(e.g. balloon drivers, paravirtualized spinlocks). Running containers in -distinct virtual machines can provide great isolation, compatibility and -performance (though nested virtualization may bring challenges in this area), -but for containers it often requires additional proxies and agents, and may -require a larger resource footprint and slower start-up times. - - - -**Rule-based execution**, such as [seccomp][seccomp], [SELinux][selinux] and -[AppArmor][apparmor], allows the specification of a fine-grained security policy -for an application or container. These schemes typically rely on hooks -implemented inside the host kernel to enforce the rules. If the surface can be -made small enough, then this is an excellent way to sandbox applications and -maintain native performance. However, in practice it can be extremely difficult -(if not impossible) to reliably define a policy for arbitrary, previously -unknown applications, making this approach challenging to apply universally. - - - -Rule-based execution is often combined with additional layers for -defense-in-depth. - -**gVisor** provides a third isolation mechanism, distinct from those above. - -gVisor intercepts application system calls and acts as the guest kernel, without -the need for translation through virtualized hardware. gVisor may be thought of -as either a merged guest kernel and VMM, or as seccomp on steroids. This -architecture allows it to provide a flexible resource footprint (i.e. one based -on threads and memory mappings, not fixed guest physical resources) while also -lowering the fixed costs of virtualization. However, this comes at the price of -reduced application compatibility and higher per-system call overhead. - - - -On top of this, gVisor employs rule-based execution to provide defense-in-depth -(details below). - -gVisor's approach is similar to [User Mode Linux (UML)][uml], although UML -virtualizes hardware internally and thus provides a fixed resource footprint. - -Each of the above approaches may excel in distinct scenarios. For example, -machine-level virtualization will face challenges achieving high density, while -gVisor may provide poor performance for system call heavy workloads. - -## Why Go? - -gVisor is written in [Go][golang] in order to avoid security pitfalls that can -plague kernels. With Go, there are strong types, built-in bounds checks, no -uninitialized variables, no use-after-free, no stack overflow, and a built-in -race detector. However, the use of Go has its challenges, and the runtime often -introduces performance overhead. - -## What are the different components? - -A gVisor sandbox consists of multiple processes. These processes collectively -comprise an environment in which one or more containers can be run. - -Each sandbox has its own isolated instance of: - -* The **Sentry**, which is a kernel that runs the containers and intercepts - and responds to system calls made by the application. - -Each container running in the sandbox has its own isolated instance of: - -* A **Gofer** which provides file system access to the containers. - - - -## What is runsc? - -The entrypoint to running a sandboxed container is the `runsc` executable. -`runsc` implements the [Open Container Initiative (OCI)][oci] runtime -specification, which is used by Docker and Kubernetes. This means that OCI -compatible _filesystem bundles_ can be run by `runsc`. Filesystem bundles are -comprised of a `config.json` file containing container configuration, and a root -filesystem for the container. Please see the [OCI runtime spec][runtime-spec] -for more information on filesystem bundles. `runsc` implements multiple commands -that perform various functions such as starting, stopping, listing, and querying -the status of containers. - -### Sentry - -<a name="sentry"></a> <!-- For deep linking. --> - -The Sentry is the largest component of gVisor. It can be thought of as a -application kernel. The Sentry implements all the kernel functionality needed by -the application, including: system calls, signal delivery, memory management and -page faulting logic, the threading model, and more. - -When the application makes a system call, the -[Platform](./architecture_guide/platforms.md) redirects the call to the Sentry, -which will do the necessary work to service it. It is important to note that the -Sentry does not pass system calls through to the host kernel. As a userspace -application, the Sentry will make some host system calls to support its -operation, but it does not allow the application to directly control the system -calls it makes. For example, the Sentry is not able to open files directly; file -system operations that extend beyond the sandbox (not internal `/proc` files, -pipes, etc) are sent to the Gofer, described below. - -### Gofer - -<a name="gofer"></a> <!-- For deep linking. --> - -The Gofer is a standard host process which is started with each container and -communicates with the Sentry via the [9P protocol][9p] over a socket or shared -memory channel. The Sentry process is started in a restricted seccomp container -without access to file system resources. The Gofer mediates all access to the -these resources, providing an additional level of isolation. - -### Application - -The application is a normal Linux binary provided to gVisor in an OCI runtime -bundle. gVisor aims to provide an environment equivalent to Linux v4.4, so -applications should be able to run unmodified. However, gVisor does not -presently implement every system call, `/proc` file, or `/sys` file so some -incompatibilities may occur. See [Compatibility](./user_guide/compatibility.md) -for more information. - -[9p]: https://en.wikipedia.org/wiki/9P_(protocol) -[apparmor]: https://wiki.ubuntu.com/AppArmor -[golang]: https://golang.org -[kvm]: https://www.linux-kvm.org -[linux]: https://en.wikipedia.org/wiki/Linux_kernel_interfaces -[oci]: https://www.opencontainers.org -[runtime-spec]: https://github.com/opencontainers/runtime-spec -[seccomp]: https://www.kernel.org/doc/Documentation/prctl/seccomp_filter.txt -[selinux]: https://selinuxproject.org -[uml]: http://user-mode-linux.sourceforge.net/ -[xen]: https://www.xenproject.org |