REST stands for REpresentational State Transfer. REST is an architecture style for designing networked applications. It is based on stateless, client-server, cacheable communications protocol. Although not based on http, in most cases, the HTTP protocol is used. In contrast to what some others write or say, REST is not a standard.
RESTful applications use HTTP requests to:
Hence REST uses HTTP for the four CRUD operations:
As part of the HTTP protocol we have methods such as GET, PUT, POST, and DELETE. These methods can than be used to implement a REST service. As REST introduces collections and items we need to implement the CRUD functions for them. The semantics is explained in the Table illustrationg how to implement them with HTTP methods.
| URL | GET | PUT | POST | DELETE |
|---|---|---|---|---|
| http://…/resources/ | List the URIs and perhaps other details of the collection’s members. | Replace the entire collection with another collection. | Create a new entry in the collection. The new entry’s URI is assigned automatically and is usually returned by the operation. | Delete the entire collection. |
| http://…/resources/item17 | Retrieve a representation of the addressed member of the collection, expressed in an appropriate Internet media type. | Replace the addressed member of the collection, or if it does not exist, create it. | Not generally used. Treat the addressed member as a collection in its own right and create a new entry within it. | Delete the addressed member of the collection. |
Source: https://en.wikipedia.org/wiki/Representational_state_transfer
Now that we have outlined the basic functionality that we need, we lke to introduce you to Eve that makes this process rather trivial. We will provide you with an implementation example that showcases that we can create REST services without writing a single line of code. The code for this is located at https://github.com/cloudmesh/rest
This code will have a master branch but will also have a dev branch in which we will add gradually more objects. Objects in the dev branch will include:
;You may want to check our active development work in the dev branch. However for the purpose of this class the master branch will be sufficient.
First we havt to install mongodb. The instalation will depend on your operating system. For the use of the rest service it is not important to integrate mongodb into the system upon reboot, which is focus of many online documents. However, for us it is better if we can start and stop the services explicitly for now.
On ubuntu, you need to do the following steps:
TO BE CONTRIBUTED BY THE STUDENTS OF THE CLASS as homework
On windows 10, you need to do the following steps:
TO BE CONTRIBUTED BY THE STUDENTS OF THE CLASS as homework, if you
elect Windows 10. YOu could be using the online documentation
provided by starting it on Windows, or rinning it in a docker container.
On OSX you can use homebrew and install it with:
brew update
brew install mongodb
Note
In future we may want to add ssl authentication in which case you may need to install it as follows:
brew install mongodb --with-openssl
We have provided a convenient Makefile that currently only works for OSX. It will be easy for you to adapt it to Linux. Certainly you can look at the targes in the makefile and replicate them one by one. Improtaht targest are deploy and test.
When using the makefile you can start the services with:
make deploy
IT will start two terminals. IN one you will see the mongo service, in the other you will see the eve service. The eve service will take a file called sample.settings.py that is base on sample.json for the start of the eve service. The mongo servide is configured in suc a wahy that it only accepts incimming connections from the local host which will be suffiicent fpr our case. The mongo data is written into the $USER/.cloudmesh directory, so make sure it exists.
To test the services you can say:
make test
YOu will se a number of json text been written to the screen.
The example demonstrated how easy it is to create a mongodb and an eve rest service. Now lets use this example to creat your own. FOr this we have modified a tool called evegenie to install it onto your system.
The original documentation for evegenie is located at:
However, we have improved evegenie while providing a commandline tool based on it. The improved code is located at:
You clone it and install on your system as follows:
cd ~/github
git clone https://github.com/cloudmesh/evegenie
cd evegenie
python setup.py install
pip install .
This shoudl install in your system evegenie. YOu can verify this by typing:
which evegenie
If you see the path evegenie is installed. With evegenie installed its usaage is simple:
$ evegenie
Usage:
evegenie --help
evegenie FILENAME
It takes a json file as input and writes out a settings file for the use in eve. Lets assume the file is called sample.json, than the settings file will be called sample.settings.py. Having the evegenie programm will allow us to generate the settings files easily. You can include them into your project and leverage the Makefile targets to start the services in your project. In case you generate new objects, make sure you rerun evegenie, kill all previous windows in whcih you run eve and mongo and restart. In case of changes to objects that you have designed and run previously, you need to also delete the mongod database.
Naturally it is of advantage to have in cms administration commands to manage mongo and eve from cmd instead of targets in the Makefile. Hence, we propose that the class develops such an extension. We will create in the repository the extension called admin and hobe that students through collaborative work and pull requests complete such an admin command.
The proposed command is located at:
It will be up to the class to implement such a command. Please coordinate with each other.
The implementation based on what we provided in the Make file seems straight forward. A great extensinion is to load the objects definitions or eve e.g. settings.py not from the class, but forma place in .cloudmesh. I propose to place the file at:
.cloudmesh/db/settings.py
the location of this file is used whne the Service class is initialized with None. Prior to starting the service the file needs to be copied there. This could be achived with a set commad.