envhttpd

A Dockerized HTTPD to Serve Environment Variables

A docker image of a web server that delivers environment variables as JSON and discrete curl-able endpoints; weighing in at less than 1mb, it is ideal to use as a queryable pod metadata sidecar in Kubernetes, or any situation in which you need to expose simple data without a lot of overhead.

Usage

Local testing

Fire up a container and curl against it...

$ docker run -e foo=bar -e yo=bro -p 8111:8111 -d kilna/envhttpd
f92be2e047b1bf68ce7c82a7b8c3358e9b4fceb0e826df6b3952c651d25096e1

# Get all included environment variables as a JSON dictionary
$ curl localhost:8111
{
  "foo": "bar",
  "yo": "bro"
}

# Get a specific value individually
$ curl localhost:8111/foo
bar

Kubernetes

See the kubernetes example for pod and sidecar deployment under the kubernetes/ folder.

Configuration

Environment Variables

You can pass in the following environment variables to configure envhttpd

ENVHTTPD_PORT: Which TCP port to run the web server on
ENVHTTPD_INCLUDE: A bar-delimited list of shell glob matching patterns for environment variables to be served from the web server. Defaults to *, which will match any environment variable not on the ENVHTTPD_EXCLUDE
ENVHTTPD_EXCLUDE: Likewise, a bar-delimited list of globs for variables to exclude from being served. Defaults to excude common system and envhttpd variables.

/etc/envhttpd.conf

Likewise there are counterparts to the above environment variables in /etc/envhttpd.conf called port, include and exclude. You can provide values by mounting your own configuration file to this path. ENVHTTPD_* environment variables will override those provided in the conf file.

# What port number to run the HTTP server on
port=8111

# Which environment variables to include, shell style globbing, bar delimited
# This list is processed first, a variable must match in order to be output
include=*

# Which environment variables to exclude, shell style globbing, bar delimited
# This list is processed second, a variable cannot match this list to be output
# Default is all base system variables along with ENVHTTPD_*
exclude=HOME|HOSTNAME|PATH|PWD|ENVHTTPD_*

Known Issues / Caveats

All content (even JSON) is served as text/plain, it is a limitation of busybox httpd that only one index file can be created. I may switch to CGI at a later point to remedy.
Special characters will be stripped from environment variable names for direct endpoints.

Author

Kilna, Anthony kilna@kilna.com

kilna / envhttpd