hello-zedcloud

The application

hello-zedcloud

hello-zedcloud is a small web server that can serve static files (HTML, etc.) from a directory in the local file system.

It is packaged as a container image that then can be used as a demo / example application to be deployed through ZEDEDA Cloud to run on an edge-node.

Instead of using a classic solution (e.g. nginx) hello-zedcloud is a small program written in Go. The reason for this is that we can quickly implement some additional features in the web server, to demonstrate various features of ZEDEDA Cloud & of EVE-OS.

Features

Static File Serving

The server serves static files (HTML, CSS, JavaScript, images, etc.) from a configurable directory (default: ./static).

Special Endpoints

The web server provides several special endpoints under the /_/ path:

• /_/version (GET) - Returns the web server version.

• /_/env (GET) - Returns all environment variables of the web server process. Useful for example in combination with https://help.zededa.com/hc/en-us/articles/18691668817179-How-to-add-environment-variables-to-edge-applications. Requires authentication if enabled.

• /_/logs (GET) - Returns all logs of all previous requests received by the web server. The web server also logs to stdout. Requires authentication if enabled.

• /_/crash (DELETE) - Causes the web server process to exit with an error. The request MUST be an HTTP DELETE with a query param areYouSure=YesIAmSure. Optionally, specify the exit code with exitCode query param (default: 77). Example: curl -X DELETE "http://localhost:10080/_/crash?areYouSure=YesIAmSure&exitCode=42" Requires authentication if enabled.

• /_/alloc (POST) - Causes the server to allocate memory. The size query param specifies how much memory in bytes (supports KB, MB, GB suffixes). This can be used to allocate memory until the OOM killer terminates the process, simulating an application issue. The server periodically walks the allocated memory to prevent garbage collection. The optional delay query param controls CPU usage during memory walking (supports ms, s suffixes, default: 200ms). Example: curl -X POST "http://localhost:10080/_/alloc?size=500MB&delay=100ms" Requires authentication if enabled.

• /_/stats (GET) - Returns Go runtime statistics including CPU time and allocated memory. NOTE: These values cannot be directly compared with per-process Linux kernel statistics.

• /_/echo (ANY) - Returns a complete dump of the HTTP request, including headers and body.

• /_/upload (POST) - Accepts a multipart file upload and saves it locally. Files are stored in <static-dir>/_/uploads/<upload-id>/ with the original filename preserved (after sanitization). The response includes the file path, size, and SHA256 checksum of the uploaded file. Not very useful for file upload itself, but can be used to simulate traffic towards an edge-app instance (similar to if the edge-app would download a file). This is subject to any bandwidth limit configured for the server. Example: curl -X POST -F "[email protected]" http://localhost:10080/_/upload Requires authentication if enabled.

• /_/uploads (GET) - lists all uploaded files in the uploads directory and displays them as an HTML page with download links. Requires authentication if enabled.

HTTP Basic Authentication

The server supports HTTP Basic Authentication for protecting sensitive endpoints. Authentication can be configured via CLI flags or environment variables:

• By default, random credentials are generated and displayed at startup
• Set --username="" (empty string) to disable authentication entirely
• Use --username=myuser --password=mypass for custom credentials
• Use --username=$RANDOM --password=$RANDOM to generate random credentials

When authentication is enabled, the following endpoints require credentials: /_/env, /_/logs, /_/crash, /_/alloc, /_/upload

Bandwidth Limiting

The server can be started with a global bandwidth limit using the -bw-limit CLI flag. This applies a rough bandwidth limit to both read and write operations (each independently, not combined). Concurrent requests share this bandwidth limit. This is useful to simulate slow network connections, for example when using this server as a local HTTP datastore to serve images to an EVE-OS instance.

Supported formats: 2m, 2mb, 2M, 2MB (all meaning 2 megabytes per second) Default: 2GB/s (effectively unlimited in most scenarios)

Configuration Options

The server can be configured via CLI flags or environment variables:

Note: CLI flags take precedence over environment variables.

The Zedcloud deployment

TODO, see ./zedcloud_deployment.