BitMail Live - try logging in. When a new user logs in for the first time, (s)he is created with the password provided.
Click here - to see how the system is built, tested and deployed.
Background - a few words about me and web development.
This section describes the conceptual idea and the design choices for a scalable and reliable e-mail service.
The concept is a high reliable e-mail sending service. The service is a container that employes several Mail Transport Agent Providers (MTA Provider). A single point of e-mail submission is offered by the container. When an e-mail is submitted to the service it schedules a provider and forwards the e-mail to it. If a transport fails one of the other providers is used as fail-over. If no MTA provider is availble the e-mail service logs that it is down and terminates entirely.
To provide a way of sending e-mails the system offers a simple web-mail interface over https. The interface allows the user to log in and compose e-mails. Multiple recipient are supported by separating their address with semi-colon.
This is a full stack implementation of an e-mail service using several sending providers. See the
systems component diagram below.
The solution is implemented in four tiers divided between a server and a client. Three of the tiers run on the server while the final tier is a browser on the client. At back of the server we have the MTAServer which is an application implementing the MTA Container. In the middle is the BackEndServer which handles access to the storage. The front of the server, the ClientAPI, accepts HTTPS connections from browser clients. Server applications are written in the Go language while the client is written in Dart compiled to JavaScript.
An MTA-container runs with multiple MTA-provider-components inside to offer a unified API for sending (and receiving) emails. Also, it ensures reliability through fail-over if any MTA-provider should have a fall-out. The MTA Container uses a Scheduling strategy for chosing which MTA provider it shall employ. By default a Round Robin Scheduler is provided. Performance can be optimized by providing a custom instance of the Scheduler-strategy interface. For example, one could implement an adaptive scheduling strategy sending e-mails according to performance stats (e.g. slow MTAs gets scheduled less often).
The system supports three MTAs for sending e-mail: Amazon SES, MailGun, and SendGrid. All three providers offer Go-libraries to access their services.
The BackEndServer listens for incoming connections from the ClientAPI (the next tier towards the client). It uses the storage for user names and other log in related information when authenticating e-mail send requests. The storage is Json-based. Entries are maps from string to string. The storage offers three operations: put, update, and get. Lookup takes a map from string to string and returns all maps in storage that have the given map as a subset. See jsonstore.go The storage container only supports in memory storage for the time being. A final version should include permanent storage like a Oracle MySQL database to implement the jsonstore. A high-performing solution might employ a file based solution in a High-Perf-Distributed-File-Systems like Hadoop HDFS. The storage is used
The ClientAPI is a Https-webserver which serves the client. Also, Ajax requests are handled by taking appropriate actions with the BackEndServer and the MTAServer. As an example when a users logs in the ClientAPI queries the BackEndServer to authenticate.
On the client side a Dart-application renders the user interface. It implements the Model-View-Controller pattern having the View defined in index.html, the Controller defined in main.dart and a model defined in mailmodel.dart. The model takes a strategy for handing communication with the ClientAPI, see ClientAPI class.
This design has decoupled components in order to scale well. A deployed instance of the system may include several MTAServers, and ClientApis running on different machines. However, to give a consistent experience a common storage is needed, and therefore all ClientAPIs need access to the same BackEndServer. We do provide a Proxy interface for supplying a ProxyStore where the idea is that one instance will have the actual physical storage while other BackEndServer servers could use a Proxy.
To try out the application in practice the domain mail.bitlab.dk has been set up. The servers use a self signed SSL-certificate, please ignore the browser warnings and proceed to visit the site or install the certificate beforehand. The domain is supported by two servers: mail0.bitlab.dk hosted in Aarhus, Denmark and mail1.bitlab.dk hosted by Amazon AWS in Oregon west.
The build system uses a Python based tool called Fabric. It enables one shell-command to build, test, commit and deploy new changes to the code base. This gives a short cycle from code to new running features. To get an idea of how this works you can try it out by logging in at the build-server. The start-up-password is required to log in, for help with you can also contact [email protected].
ssh [email protected]
cd e-mail-service
ls
Here you will see this repository checked out. The machine is also setup with SSH-Private keys to allow it to deploy new versions of the software to mail0.bitlab.dk and mail1.bitlab.dk. Try it:
fab deploy_bitlab_servers
Fabric will execute commands locally to build and test the workspace. Then, it uses ssh to upload files and execute the necessary commands on the remote server to stop the running version and replace it. To get an overview of what it does see fabfile.py. The deploy function near the bottom lays out what is going on. Old versions are kept on the servers until someone logs-in and manually deletes them or reenables them in case of a faulty deployment.
See the Live Demo here.
To get, build, test and deploy the code yourself you need to follow the steps below.
Clone this repo.
You must be running on Linux or OSX and you need the following tools installed :
- Python 2.17
- pip (to install Fabric do pip install Fabric)
- Fabric
- GoLang-SDK 1.5
- DartLang-SDK ^1.12.1
- some scripts use
realpath
On OSX you can try the bootstrap.sh script.
Change directory to e-mail-server and type:
e-mail-service$ fab build
Fabric builds it all, invoking both the Dart and Go build systems as needed. Notice how
go getand
pub getget all the Go and Dart dependencies.
We only have tests for the components written in Go. To run the Go test suite:
e-mail-service$ cd goworkspace && go test
Or use Fabric
e-mail-service$ fab test
Note that the MTA-Providers sending mails via thirdparty libraries are tested semi-manually. Fabric helps running the test commands which will query for an e-mail address accessible by the tester. Failure/success is determined by whether an e-mail was sent to this address.
e-mail-service$ fab test_manual
This will update the production system at mail.bitlab.dk provided you have got the SSH-RSA private keys to access the servers.
fab deploy_bitlab_servers
The ssh-keys needed are avaible in the
[email protected]:.ssh/ec2key.pemfile on the test development environment. As stated above you can log in with
[email protected]using the start-up-passphrase given in submission note.
I have been working fulltime with software development in C/C++, Java and C# on the windows platform from 2008 - 2011. My prior experience with Web-development dates back to 2005-2007 where I maintained a webpage for the Tutor-association at Aarhus University running on a LAMP-box.
I have no prior experience with the Go language before this exercise.
- NewLines in message resulted in invalid JSon sent from the browser. Fixed by sending Base64 encoded body
- Using Screen for running server processes didn't always replace running server-processes properly, now we use disown and pipes to log-files for running the servers and kill -9 to stop them.
- Fabric build updated with stage_deploy target for testing on dev.bitlab.dk.