VF2L: Nginx

 Intro

Previously I have found that Docker works well on VF2L even though the server is not very powerful.  VF2L doesn't include Docker-Compose and it was educational for me to use command line tools.  There are limited pre-packaged images available for risc-v, but this isn't an issue as Alpine, Debian or Ubuntu can be used as a basis for installing software packages.

VF2L is convenient to use as a testing ground and I decided to try out nginx here even though I could use Docker on RPI or Windows where more docker capabilities are available (compose, desktop, OMV etc).

Proxy Servers

I don't have a good understanding of Proxy Servers.  Originally they were used so that a number of local clients could share an Internet IP address, more recently this has been replace by NAT (Network Address Translation) but proxy servers are still used by some to cache pages, filter available sites and for authentication.  This type of proxy is known as a forward proxy server. In contrast reverse proxy servers accept requests from the Internet and pass them to appropriate web / application servers for processing.  They protect internal servers from malicious users and provide SSL certificates and load balancing.  The title "proxy server" is used for either forward or reverse proxies, which can be confusing.

Nginx

Nginx is the leading proxy server used currently.  It provides a web server, reverse proxy, load balancing and caching. I noticed that it has an official Docker riscv64 image and decided to try it out on VF2L.
It was as simple as typing a docker run command to download the software and spin up a container.  I can then immediately access the nginx placeholder home page.  It only took a minute!

The nginx container runs on a stripped down debian image (126MB) and I needed to install "nano" so that I could create my own test home page in /usr/share/nginx/html/index.html.

After a little experimentation I configured a more useful container.  This has two volumes "html" for  webpages and "conf.d" for the nginx configuration file.  As these volumes are provided from VF2L I can conveniently edit the files on them outside the container then reload nginx in the container to update the configuration.
I also prefer to alpine linux (52MB) as a base over Debian for Docker servers.
As VF2L is a test server I allocated port 80 to be available for the web server. 

Nginx web server configuration

I started by creating an nginx web server.  This is very simple.  The default.conf file simply says that the server should listen on port 80 and the home page is to be found at /usr/share/nginx/html.
In my browser I enter the VF2L ip address and the container returns the ...nginx/html/index.html webpage from the server.

I added a couple of extra locations.  This provides the ability to setup separate web page mappings.

The URI http://192.168.0.25/second.html maps to ...nginx/html/second.html.
http://192.168.0.25/third/ maps to ...nginx/html/third/index.html.
I found it a little confusing that nginx adds in the location (e.g. /third/ ) to URI but this is useful.

nginx proxy server

Setting up a proxy server is just as easy.  I added a location /pi/ in my server configuration and specified using the proxy_pass argument that requests should be directed to my application server (192.168.0.41).

I also had to add a folder ..../pi/ on my application server containing the web page.

Now the request http://192.168.0.25/proxy/ returns the web page ...html/pi/index.html

nginx is also kind enough to allow you to setup multiple web servers in a single instance. I setup a second VF2L server on port 8080.

A request http://192.168.0.25/proxy/  is directed to "myproxied" and the page /usr/share/nginx/html/proxy/index.html is returned.

External Access

Of course the main purpose of a reverse proxy is to route requests coming from outside the local network.  As a test I setup my router to forward port 8080 to VF2L.  

Now I can enter my external ip address and add "/pi/".  My router sends the request to VF2L which looks at "/pi/" and forwards it to //PI41 which returns the web page html/pi/index.html.

Outro

This experimentation with nginx gives me some basic practical understanding of reverse proxies.  They are particularly useful for docker containers as there may be many http(s) ports in use on different containers and nginx can forward requests to the appropriate destination for processing.

There is a load more functionality which I can look at in nginx (SSL in particular) and I haven't created anything of long-term usefulness.  This sets me up well to use nginx with other docker applications, in the first instance this could be an opencloud or nextcloud server.

Python can replace BAT

 Intro

For a long while I have put up with the limitations of Windows antiquated 50 year old batch file system.  With plenty of trial and error I can set up batch files to do simple tasks but it continually frustrating that they have none of the capabilitiy or power of linux shell scripts (which are even older!).  I need some better way to control BEN2 processes and I foolishly thought to try PowerShell as an alternative.  As you would expect it is horrendous, a whole new useless language to help you dig into the cesspit of Windows.

It then occured to me to use python; after all it is a scripting language, windows friendly, easy to use and has an interface to the underlying Operating System.

Serial Port Control

The arses at Microsoft have seen fit to reduce serial port functionality in Windows 11.  Windows 10 shared ports quite happily with WSL programs.  By default Serial ports are now not available within WSL.  You need to install a program called usbipd from github to attach ports to WSL. 

The instructions are not trivial.  You have to identify the correct device in a list that usbipd gives you then "bind" and "attach"  it to wsl.

This isn't something I am capable of doing within a batch file.

Python

Our python script first reads in output from the command "usbipd list" to see if it can find the COM port, which will be labelled as "USB serial converter".
If we find it we capture BUSID and STATE values for that line.

Once we have these values we can attach the device (BUSID=3-3) in this example to WSL.  The bind command only has to be done once so we dont issue it every time in the script.

Outro

Note that the BUSID can change depending on what is attached to the PC.
Also, although device 3-3 is called COM3 in Windows it is called /dev/ttyUSB0 in WSL.
Windows doesn't help me with working this out.

A very irritating situation :(

M C Escher

Intro

As a child / teenager I was fascinated by the drawings of M C Escher.  I had a book of his graphic art which I often enjoyed looking at.  Recently it occured to me that Escher doesn't seem to be well-represented in the the art world despite being well known.

I purchased a Taschen book "M.C. Escher The Graphic Work" for a few pounds on ebay.  It contains the same works I recall with much fondness from fifty years ago: tesselations; infinity representations; plausible but impossible scenes; transformation and evolution of shapes.

Escher and Penrose

Escher spent many years refining his skills creating intricate woodcuts and lithographs, mainly traditional scenes and landscapes, some of which were plausible but unreal.  At one point, whilst at a Mathematics conference, Sir Roger Penrose visited an Escher exhibition and was intrigued by his work. The interest developed into correspondence and a friendship.  Escher was very taken with Penrose's mathematical study of tesselations (patterns covering a surface) and developed them into shapes, figures and animals interlocked and transforming in space.

Penrose narrated a fascinating BBC Scotland documentery about Eschers work, "The Art of the Impossible", in 2009 and participated in an Oxford lecture on the subject. There is also a Sky Arts documentary Journey to Infinity (trailer) narrated by Stephen Fry. It turns out that Eschers interest in repeated surface patterns was stimulated by a visit to the Alahambra in Granada, Spain.  I have also visited and been enthralled by these patterns both at the Alahambra and in Marrakesh, Morocco.  

The Art World

Escher considered himself a graphic artist working in wood and metal.  He had no mathematical or scientific education but had some deep intrisic understanding and the ability to translate these ideas into a visual form with fantastic technical skill.
He has been completely overlooked or ignored by the art world with practically no works on display or public exhibitions.  His works certainly qualify as good art in my understanding: great technical skill; the ability to communicate significant ideas; thought provoking concepts. There are a number of 20th Century "geometric" art movements during the period he was working as well as surrealism and its derivitives.

I think he was insufficiently "arty" and certainly didn't promote himself as unique visionary whose work you needed to buy.  Perhaps the traditional techniques of woodcut and lithography were not trendy, or the ability to make hundreds of prints from a woodcut lowered their value and interest to collectors.
He was popular with the public during the "hippy" sixties and seventies with work featured on a number of album covers.  I  predict he will become more appreciated in future.

Favorites

I have tried to identify my favorite works but I find it difficult as they cover a number of different subjects and techniques.  For the list below I have chosen those which stick in my mind most clearly.  Images are taken from "M C Escher The Graphic Work", but I found "Kaleidocycles" and "The World of MC Escher" interesting.

Docker on Risc-V

 Intro

My most recent  Risc-V development board is the VisionFive 2 Lite.  It isn't particularly powerful, but is probably similar to a RPI-3.

Interestingly the VF2L image comes with docker included.
I decided it would be useful to see how this compares with my other docker setup PI43+OMV

Images Available

There is an Docker Official Index of 48 riscv64 images as of January 26.  There are various programming languages (Go, Ruby, Perl, python etc), a few OS guests (Debian, Ubuntu, Alpine), some webservers (Apache httpd, tomcat, nginx) and some others mainly technical utilities and a few applications (e.g. nextcloud).

Other examples have been created, usually, they are geared towards multiple architectures and include riscv64.  For example I wanted a container I can SSH into so I googled "docker riscv64 ssh" and found woahbase/alpine-ssh.

This is based on the alpine docker image.  I ran the image to build a container and I was able to ssh in to use it.  This is excellent.

An alpine image is only 7MB size and including SSH only increase it to 14MB.

Docker doesn't create a complete VM, it uses the linux host kernel and syscall interface to provide an environment.

Alpine linux comprises a minimal set of utilities to make it useful, so it combines well with docker and is widely used.

Add applications to an image

Previously on my PI43:OMV server I have used docker compose to create images.  I have pasted in configurations and used compose to build an image and run the container.  I dont have docker compose or "standard" images on VF2L so I need to think and learn a little bit more about docker.

For my images / containers I start off from a minimal Alpine Image. I run this image as a container and I can access the container through a shell, enabling me to install software, create files, bring up Services etc.  

My first experiment was to create an Alpine lighttpd container.  I started by running a "raw" alpine:3.23 image.

I needed to add the openrc package plus a couple of extra commands allowing me to start services (this is a wrinkle in alpine setup).

I could then add the lighttpd package and start the web server on port 80.

In a web browser I can see the lighttpd installation placeholder page.

Create a lighttpd image

Now I know how to configure a container running a lighttpd webserver I need to create a new image including lighttpd which I can start up as a web server.

To do this I create a "Dockerfile" which contains commands to execute whilst building the image.  These can include software installation using the Alpine "apk add" command and bringing up Services.  A working image includes all necessary software (executables, configuration files, working storage etc).  Based on the interactive setup I used the Dockerfile as shown here to build a "alpine-lighttpd" image for my webserver.

 

There is a small downside which needs to be dealt with; the raw image has no persistent storage.  The container uses temporary files for all the storage it needs and this is deleted when the container is removed.  So if I added some html files to the container they would be lost when I removed the container.

The answer is to create one or more volumes to contain our data.  For my lighttpd web server the home page will be stored at /var/www/localhost/htdocs/index.html.  with the command "docker create volume VarWwwLocalhost" I created a volume.  I then mapped the volume to the home page directory in my docker run command which starts the container.

Now I could add index.html and other web pages within the container and they remain available each time the container is loaded.

In fact I can also access the volume from VF2L outside the docker container so I can look at or edit files from VF2L before starting the container.  My first effort is shown below.

A vital feature of docker is that it allows you to redirect ports.  When I run the lighttpd container I specify that I want to map VF2L port 8080 to my container port 80.  Then any URL which specifies port 8080 is directed to the container port 80.

Outro

It is very useful to be able to create my own images or amend standard images for my requirements.  Docker is an excellent tool for making these images and running the associated containers.  VF2L has proved itself capable of running docker and docker containers.  It is wonderful to separate the host OS linux from the image so that I am in total control of the container.  VF2L runs StarFive linux but my images are built on alpine, but they could be built on Debian or Ubuntu.

So far I have built containers for lighttpd (described above) and for ssh access so that I can ssh into a test alpine server.  I have also quickly started up nginx and nextcloud containers to experiment with them.  I am quite amazed at how quick and easy it can be to start a complete application.  If there is an appropriate image it is much simpler than adding linux packages to the operating system and configuring them.