Eclipse Zenoh

The Eclipse Zenoh: Zero Overhead Pub/sub, Store/Query and Compute.

Zenoh (pronounce /zeno/) unifies data in motion, data at rest and computations. It carefully blends traditional pub/sub with geo-distributed storages, queries and computations, while retaining a level of time and space efficiency that is well beyond any of the mainstream stacks.

Check the website zenoh.io and the roadmap for more detailed information.

Web Server plugin

The Web Server plugin implements an HTTP server mapping URLs to zenoh keys.
This plugin can be used to set-up a Web server where the resources are retrieved from geo-distributed zenoh storages, each leveraging various backends (file system, database, memory...).

Library name zenoh_plugin_webserver

:point_right: Download stable versions: https://download.eclipse.org/zenoh/zenoh-plugin-webserver/

:point_right: Build "main" branch: see below

:warning: Documentation for previous 0.5 versions:

The following documentation related to the version currently in development in "main" branch: 0.6.x.

For previous versions see the README and code of the corresponding tagged version:

• 0.5.0-beta.9
• 0.5.0-beta.8

Examples of usage

Assuming you have a static website, you can:

• expose the files as zenoh key/values using the File System backend
• set-up this Web Server plugin that will allow HTTP clients to browse the files.

Here are the steps:

1. Make sure the libraries for the File System backend and the Web Server plugin are available for the zenoh router:
   either installing their packages (depending your platform), either downloading the library files corresponding to your platform in your ~/.zenoh/lib directory.

2. Copy the website files into a ~/.zenoh/zbackend_fs/my-site directory (or make it a symbolic link to the path of your website)

3. Create a zenoh.json5 configuration file containing:

   {
     plugins: {
       webserver: {
         http_port: 8080,
       },
       storage_manager: {
         volumes: {
           fs: {}
         },
         storages: {
           demo: {
             key_expr: "my-site/**",
             strip_prefix: "my-site",
             volume: {
               id: "fs",
               dir: "my-site",
               read_only: true
             }
           }
         }
       }
     }
   }
   

4. Start the zenoh router (zenohd). It will automatically load the Web Server plugin and make it available on port 8080. It will also create a storage replying to any zenoh query on key expressions starting with my-site/.
   Now you can browse your site on http://localhost:8080/my-site.

For more advanced use cases you can also:

• Have the files of your web sites stored on different hosts. Running a zenoh router with a File System Storage on each host allow to make all the files available under the my-site/ zenoh key.
• Duplicate the files of your web sites on several hosts to provide fault tolerance.
• Start several zenoh routers with the Web Service plugin on different hosts (not necessarly the same than the hosts running the File System storages). Each host will serve your web site.
• Use other backends than the File System to store your resources and make them available through zenoh. (List of available backends here).
• Deploy a zenoh application that will implement eval function for a resource, replying to requests with a dynamic content (see the z_eval example in Rust or Python).

Configuration

In its configuration part, the plugin supports those settings:

• http_port - int or string - required:
  either a port number as an integer or a string, either a string with format "<local_ip>:<port_number>"

Troubleshooting

Address already in use

If in zenohd logs you see such error log at startup:

[2021-04-12T14:20:51Z ERROR zenoh_plugin_webserver] Unable to start http server for REST : Os { code: 48, kind: AddrInUse, message: "Address already in use" }

It means another process is already using this port number that the webserver plugin would like to use. In such case, you have 2 solutions:

• stop the other process using this port
• make the webserver plugin to another port changing its listener option.

Permission denied

If in zenohd logs you see such error log at startup:

[2021-04-12T13:55:10Z ERROR zenoh_plugin_webserver] Unable to start http server for REST : Os { code: 13, kind: PermissionDenied, message: "Permission denied" 

It probably means your OS (this usually happens on Linux) forbids the usage of the configured port for non-root user (actually it usually restricts all ports between 0 and 1024). In such case, you have 2 solutions:

• run zenohd with root privileges (via sudo)
• use another changing he webserver plugin's listener option.

How to build it

:warning: WARNING :warning: : Zenoh and its ecosystem are under active development. When you build from git, make sure you also build from git any other Zenoh repository you plan to use (e.g. binding, plugin, backend, etc.). It may happen that some changes in git are not compatible with the most recent packaged Zenoh release (e.g. deb, docker, pip). We put particular effort in mantaining compatibility between the various git repositories in the Zenoh project.

:warning: WARNING :warning: : As Rust doesn't have a stable ABI, the plugins should be built with the exact same Rust version than zenohd, and using for zenoh dependency the same version (or commit number) than 'zenohd'. Otherwise, incompatibilities in memory mapping of shared types between zenohd and the library can lead to a "SIGSEV" crash.

At first, install Cargo and Rust. If you already have the Rust toolchain installed, make sure it is up-to-date with:

$ rustup update

To know the Rust version you're zenohd has been built with, use the --version option.
Example:

$ zenohd --version
The zenoh router v0.6.0-beta.1 built with rustc 1.64.0 (a55dd71d5 2022-09-19)

Here, zenohd has been built with the rustc version 1.64.0.
Install and use this toolchain with the following command:

$ rustup default 1.64.0

And zenohd version corresponds to an un-released commit with id 1f20c86. Update the zenoh dependency in Cargo.lock with this command:

$ cargo update -p zenoh --precise 1f20c86

Then build the backend with:

$ cargo build --release -p zenoh-plugin-webserver