Solution Filter in Visual Studio allows a faster load of the solution with selective projects. When we are working on a large solution with several projects, we may not work with all the projects together. Sometimes, specific developers only focus on a set of projects. Solution Filter in Visual Studio allows us to select only the required projects… Read More »

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Episode 594

Christian Geuer Pollmann on Erlang and Elixir

Christian Geuer-Pollmann describes the Erlang ecosystem, the Elixir language, and open source Azure tools he has built with Elixir.

Links:

https://github.com/chgeuer
https://twitter.com/chgeuer
http://blog.geuer-pollmann.de

Welcome Christina Cyr, CEO of dToor and the Cyrcle Phone

• This was their 5th year at CES. Mostly hanging out at Eureka Park, which is the startup area
• 2 years ago saw companies doing encryption for voice data because of creepy speakers, now they have gone mainstream.
• Startups are only allowed to be there for 2 years.
• This year dToor got coverage on BBC, CNET, The Daily Mail
• Enclosure company didn’t finish, so Christina 3D printed
• CTA is Consumer Technology Association. $97 to join and worth it.
• Wyze cameras, selling for $19.99
• Random connections from having a booth
• Christina works out of WeWork. Previously she was at Extra Slice in Bellevue, wanted a landline (LAN connection) for older builds of linux
• Metrix Create, Sodo also shut down
• Volunteers at their booth:
  • Aileen McGraw, WeWork Labs Manager
  • Xuny Haley, CoMotion Labs Manager
  • Nalin Chuapetcharasopon, Crowdfunding Expert
  • Anna Chuapetcharasopon, EdTech Consultant
• Former guest Scotty Allen dropped by.
• How did this phone get started?
• Phone wasn’t fitting in a pocket in 2014
• People wouldn’t take cardboard prototypes seriously
• Decided to use Seeed Studio’s phone kit with a different “skin”
• Presented as a phone for women, that was a mistake
• Featured in the telegraph out of context
• Demographics were 50/50
• Marketing tech products to women
• Apple Watch is taking the place of similar kind of role
• Joel Telling (3D printing nerd) goes to the hospital, after his watch alerted him to tachycardia
• Unity (software)
• The 4G version of the phone has
  • Dual SIM
  • Two headphone jacks
  • Qualcomm Snapdragon
  • Transitioning from micro-b to USB-C
• Working with vendors
• 4 vendors that have the snapdragon
• Tier 1 and Tier 2 companies
• Vendors want to hear 100K units
• Navigating working with vendors
• Looking at doing testing in China for FCC
• Dealing with Tariffs, as batteries and LCDs are coming directly from suppliers
• CES Tech Talk – Caught in the Crossfire: How Tariffs Impact Tech with Austere Sage Chandler, Vice President—International Trade, Consumer Technology Association (CTA)
• Harmonized Tariff Code 
• Different goods have different Tariffs
• Should have been an LLC instead of an S Corp or C Corp
• NRE for a completely custom display is $6M!
• Circular display is off the shelf, with 800×800 outer dimensions
• The 4G LTE phone will have a “tangential foot” (see image below)
• Module comes with Android 9
• Christina put together a document for hardware startups in Seattle, might be useful to listeners even if not in Seattle
• Cyrclephone.com
• @CyrChristina

Download audio: http://traffic.libsyn.com/theamphour/TheAmpHour-475-ChristinaCyr.mp3

Git is an important part of daily programming (especially if you're working with a team) and is widely used in the software industry. Since there are many various commands to use, mastering Git takes time but some commands are being used more frequently (mostly daily) and in this post, I

There are many solutions for creating a local test Kubernetes environment, such as minikube or MicroK8s, but a new project called KIND offers a fresh approach that may interest Kubernetes developers and administrators.

KIND stands for Kubernetes IN Docker, and as the name suggests, it creates a Kubernetes cluster using Docker to host the nodes. This is a novel approach, that takes advantage of Docker’s easy, self-contained deployments and cleanup to create the test Kubernetes infrastructure.

KIND Installation

Make sure you have Docker and Go installed, and then install KIND with the command:

GO111MODULE="on" go get sigs.k8s.io/kind@v0.6.1

This will place the kind executable in the directory $GOPATH/bin/kind, which will be ~/go/bin/kind by default.

Assuming the Go bin directory is in the PATH, build a test cluster with the command:

kind create cluster --name mycluster

The first cluster takes a little while to download KIND Docker images, although subsequent clusters take less than a minute to create.

KIND will add the new cluster details as a context to your ~/.kube/config file, so you can test the cluster is up and running with the command:

kubectl cluster-info --context kind-mycluster

You can set this context as the default with the command:

kubectl config use-context kind-mycluster

Using the KIND Kubernetes cluster

The most immediate issue I ran into when using KIND was accessing the services deployed to the cluster.

By default KIND only exposes the Kubernetes API server. This means kubectl will work as expected. So you can deploy to the cluster and query resources, but accessing your services requires some extra work.

A solution is to use kubectl as a proxy:

kubectl proxy --port=8080

Kubernetes services are then available through a specifically formed URL like http://localhost:8080/api/v1/namespaces/default/services/webserver:http-web/proxy/.

The Kubernetes documentation has more details on these proxy URLs:

To create proxy URLs that include service endpoints, suffixes, and parameters, you simply append to the service’s proxy URL: http://kubernetes_master_address/api/v1/namespaces/namespace_name/services/[https:]service_name[:port_name]/proxy

Port forwarding removes the need to construct special URLs. Start port forwarding with a command like:

kubectl port-forward svc/webserver 8081:80

The service is now available on the local port of 8081, directing traffic to the service port 80. This means the URL http://localhost:8081 can be used to access the service.

You can also use port forwarding on an ingress controller:

kubectl port-forward svc/nginx-release-nginx-ingress 8081:80

This command allows you to access services via any ingress rules you have configured.

The KIND documentation also provides some additional details on how to expose ingress controllers for a more permanent solution.

First impressions

Once I got around the issue of accessing my services, KIND performed remarkably well for a beta release. External tools like Helm worked fine, and I could deploy custom dashboards to the cluster.

I appreciated the fact the KIND was so self-contained. Because everything is a Docker container, creating the cluster was quick, and when it was cleaned up afterward there was nothing left running on the system.

Conclusion

Getting a Kubernetes cluster running locally isn’t that difficult these days, but KIND makes it especially easy to create a cluster. Admittedly, Kubernetes running on Docker to orchestrate Docker is a little mind bending, but it can’t be beaten for convenience.

The real value of KIND is the ability to run it as part of automated tests. I didn’t have a use case for this personally, but I’m sure it lives up to the promise.

I’ll seriously consider using KIND over minikube for local testing from now on.

This tutorial is the  10th part of a series : Building microservices through Event Driven Architecture.

The previous step is about building microservices through Event Driven Architecture part9: Implementing EventSourcing on Application : http://logcorner.com/building-microservices-through-event-driven-architecture-part8-implementing-eventsourcing-on-application/

During this journey, I will  talk about how to handle updates on a Event Sourcing System.

So , in the prevoius steps , I have stored all business changes of the system as events instead of storing the current state.  and I  rebuild the current state by applying all the events to the aggregate.

I have builded a list of domain events :  business changes happened in the past expressed in the  Ubiquitous Language : ex ThePackageHasBeenDeliveredToCustomer.

Domain Events are immutable, when a event happen it cannot be changed.

So, to correct a mistake on an event, I have to create a compensation event with correct values like bank account transactions.

The aggregate records committed events and protects  business invariants. It is the transaction boundary.  To deal  with concurrency  I will use Optimistic Concurrency Control (OCC)   with versioning.

Without acquiring locks each transaction verifies that no other transaction has modified the data it has read. If not the transaction is committed,  if yes the transaction rolls back and can be restarted.

With versionning , the user reads the current state of the aggregate,  then send commands with the version number, if the version number match the version of the aggregate then the transaction is committed.

If the version number does not match the version of the aggregate, in this case it means that the data has  been updated by someone else. So the user should read again the data to get the correct version and retry.

In this tutorial, I will shwo how to update the Speech Entity. It has the following properties  : Title, Description, Url and Type.  So the update of each property is an event and should be stored on event store.

HANDLING UPDATE ON DOMAIN MODEL

HANDLING UPDATE TITLE

TEST CASE 1 : ChangeTitle  when title is null or empty should raise ArgumentNullAggregateException:

Here I will test that if the Title is NullOrEmpty then, the system should raise an exception.

TEST CASE 2 : ChangeTitle  when expected version is not equals to aggregate version  should raise ConcurrencyException:

Here I will test that if the expectedVersion is not equals to the aggregateVersion then, the system should raise an exception.

Because I create a new speech, the aggregate version is equals to zero , so if I set expectedVersion to one, the test should raise an exception.

TEST CASE 3 : ChangeTitle  with valid arguments  should apply SpeechTitleChangedEvent :

Here I will test that if no errors , then the newTitle  should be applied to the title of the speech. In other words : Speech.Title = “value of new title after updates”

 ChangeTitle  Final implementation :

The final implementation of ChangeTitle should look like this.

Very simple, I the title is not null or empty, apply a SpeechTitleChangedEvent .  The apply function sets the speech title with the value of the event title.

The code that checks the version of the aggregate was developed in the previous steps ( see the aggregateroot.cs class)

public void ValidateVersion(long expectedVersion)
{
if (Version != expectedVersion)
{
throw new ConcurrencyException($@”Invalid version specified : expectedVersion = {Version}  but originalVersion =                             {expectedVersion}.”);
}
}

HANDLING UPDATE DESCRIPTION, URL AND TYPE

ChangeDescription, ChangeUrl and ChangeType should follow the same scenario as ChangeTitle

HANDLING UPDATE ON APPLICATION

HANDLING UPDATE TITLE

TEST CASE 1 : Handling Update when Command is null  should raise ApplicationArgumentNullException :

Here I will test that if the updateCommand is null, then the system should raise an exception.

So I should mock all external dependencies : IUnitOfWork, ISpeechRepository and IEventSourcingSubscriber

TEST CASE 2 : Handling update when speech does not exist  should raise ApplicationNotFoundException:

Here I will test that if the speech to update does not exist, then the system should raise an exception.

I have to arrange my repository ao that it returns a null speech with mock  :

moqEventStoreRepository.Setup(m => m.GetByIdAsync<Domain.SpeechAggregate.Speech>(command.SpeechId))
.Returns(Task.FromResult((Domain.SpeechAggregate.Speech)null));

and that’s it.

TEST CASE  3 : Handling Update when Command is not null should update speech Title :

Here I will test that if the command is not null and the speech to update exist , then the title should be updatet.

A way to verify that the Speech Title is modified is to check it’s value before sending it to repository :

moqSpeechRepository.Verify(m =>
m.UpdateAsync(It.Is<Domain.SpeechAggregate.Speech>(n =>
n.Title.Value.Equals(command.Title)
)),Times.Once);

 

TEST CASE  4 : Handling Update when Expected version is not equal to aggregate version should raise ConcurrencyException :

Here I will test that if the expectedVersion is not equals to the aggregateVersion, then the system should raise an exception.

HANDLING UPDATE ON REPOSITORY

HANDLING UPDATE 

TEST CASE 1 : Handling Update when Speech is null  should raise RepositoryArgumentNullException :

TEST CASE 2 : Handling Update when the speech  does not exist should raise NotFoundRepositoryException 

 TEST CASE 3 : Handling Update when the speech  is valid and exist should perform update

And the final implementation

HANDLING UPDATE ON PRESENTATION

HANDLING UPDATE 

TEST CASE 1 : Update Speech When ModelState Is Invalid Should Return BadRequest :

TEST CASE 2 : UpdateSpeech When An Exception Occurred Should Raise InternalServerError

Idem with register speech (ExceptionMiddleware)

 

TEST CASE 3 : Update Speech When ModelState Is Valid With No Errors Should Return Ok

And the final implementation

 

TEST WITH POSTMAN

Hit F5 and start postman and sql server.

Let’s start sql server and see what’s going on
Here I have to table’s [dbo].[Speech] and [dbo].[EventStore] , let us run a select query , you can see that these 2 tables are empty.

Let us start postman and run a post request to create a speech : http://localhost:62694/api/speech

Ok lets go

the postman scripts are here : LogCorner.EduSync.Command\src\Postman\BLOG.postman_collection.json

Now I should have a newly created speech and a event LogCorner.EduSync.Speech.Domain.Events.SpeechCreatedEvent, LogCorner.EduSync.Speech.Domain, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null
Note that the version is equals to 0.
For each new speech, the version should be equal to zero.

If I inspect the payload, I must see my event

 

{
“Title”: {
“Value”: “Le Lorem Ipsum est simplement du faux texte”
},
“Url”: {
“Value”: “http://www.yahoo_1.fr”
},
“Description”: {
“Value”: “Le Lorem Ipsum est simplement du faux texte employé dans la composition et la mise en page avant impression. Le Lorem Ipsum est le faux texte standard de l’imprimerie depuis les années 1500, quand un imprimeur anonyme assembla ensemble des morceaux de texte pour réaliser un livre spécimen de polices de texte”
},
“Type”: {
“Value”: 3
},
“AggregateId”: “7c8ea8a0-1900-4616-9739-7cb008d37f74”,
“EventId”: “a688cc8a-ed56-4662-bbad-81e66ed917a0”,
“AggregateVersion”: 0,
“OcurrendOn”: “2020-01-19T15:49:59.3913833Z”
}

 

To update the title of the speech, i run the following request http://localhost:62694/api/speech
it is a put request .

I grab the identifier of the newly created speech CF17D255-9991-4B7B-B08E-F65B54AA9335
Let us copy from sql and paste it on request body.

Ok, Now i can run the put query

Come back to sql server to verify the result

SELECT * FROM [dbo].[Speech]

SELECT *  FROM [dbo].[EventStore]

I should see the updated title and a new event LogCorner.EduSync.Speech.Domain.Events.SpeechTitleChangedEvent.

The version should be 1 and the payload should be the update event

{
“Title”: “UPDATE_1__Le Lorem Ipsum est simplement du faux texte”,
“AggregateId”: “7c8ea8a0-1900-4616-9739-7cb008d37f74”,
“EventId”: “de253f69-ea89-4a54-8927-e09553cc43c7”,
“AggregateVersion”: 1,
“OcurrendOn”: “2020-01-19T15:55:14.1734365Z”
}

Cource code of this article is available here  (Feature/Task/EventSourcingApplication)

https://github.com/logcorner/LogCorner.EduSync.Speech.Command/tree/Feature/EventSourcingHandlingUpdates

Regards

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