DEV Community: Oleksii Kraievyi

Today, I decided to use vim in my day to day job

Oleksii Kraievyi — Mon, 22 Jun 2020 10:17:04 +0000

This weekend, I was really inspired to start doing something new . I've been watching lots of cool videos about shell and different command line utilities so I've blown the dust out of my Windows Terminal and installed zsh and decided to use vim as the code editor.

https://github.com/ohmyzsh/ohmyzsh

With powerlevel10k theme

https://github.com/romkatv/powerlevel10k

Once installed, edit .zshrc file

ZSH_THEME="powerlevel10k/powerlevel10k"

And for vim I used vimtutor for learning and ideavim plugin for my JetBrains Rider (i can't really refuse to use code completion and cool refactorings, sorry for that)) )

Next week, I will write a small review about my experience with vim. Stay tuned

Events immutability problem

Oleksii Kraievyi — Mon, 15 Jun 2020 13:34:14 +0000

Hope, you all know the event sourcing. And one of its core principles, that events should be never changed or deleted. But what if you really need it ?
What problem do we have ? For example, you have a User aggregate. And this aggregate should receive UserCreated event.

{ type : "UserCreated", "version" : 1, "id" : 123, "name" : "John", "metadata" : { "city" : "Chicago" } }

Then this events are applied on read models like this

public class UserReadModel : IApply<UserCreated>
{
    public int Id { get; private set; }
    public string Name { get; private set; }

    public void Apply(IDomainEvent<UserCreated> @event)
    {
        Id = @event.Id;
        Name = @event.Name;
    }
}

And it's working for a year or something. But then manager comes and he says that : "We need to show user city on our UI!". And you don't really know what to do, because your read models are dependent on your events and, in theory, you should support replaying all events from your event store to restore the state of your read models.

If you can't update and delete your events, you can tell your application, that if the v2 of UserCreated event appears during replaying events it should work with new field, but if the v1 appears, you should emit v2 event with new fields.

And this thing is called event upgrader.

public class UserCreatedV1ToV2EventUpgrader
{
        public IDomainEvent<UserCreated> Upgrade(IDomainEvent<UserCreatedV1> v1Event) 
=> new DomainEvent<UserCreated>(new UserCreated { Id = v1Event.Id, Name = v1Event.Name, City = v1Event.Metadata["City"] });
}

Now, event sourcing becomes a little less complicated ~~(no)~~

Dependencies in microservices world

Oleksii Kraievyi — Thu, 11 Jun 2020 15:48:18 +0000

Today we had a brainstorm meeting about how we can eliminate direct dependencies between services in our application. What inputs do we have

15-20 microservices
some of them have cyclic dependencies (service A calls service B and service B calls service A)
calls does not create anything, just getting some external data

After some brief discussions we've came up with some solutions

We have case when we need to go to external service on each call via middleware and check if user can have an access to app and we can't really eliminate this one. We have a cache on external service , but we've also decided to introduce local cache to even have no network calls
We have cases when the validation on one service is dependent on state in another service. In this case, we decided to store local copy of this state in scope of single service. We have all needed infrastructure for integration events so it's just the matter of time. (There's also one good point, I've pulled from this meeting - "if you need to call an external service for querying, there's possibility of a bad solution. and for commands - it's completely fine to call 3-rd party services")
And the last one is just removing depedency)) What can be easier that that ? We've check a couple of our scenarios and decided that for some cases we don't even need to call external service at all since it won't affect data integrity. For example, we've queried external service to check if resource is found when we were searching data on grid. Isn't this awesome ?

So, notes are written, time to create some tech stories in jira