I need help how to think about designing our application to fit into the new Azure Service Fabric template.
Today we have an application built on Azure Cloud Services. The application is built around DDD and we have separate bounded contexts for different subsystem parts of the application. The bounded contexts are today hosted in one worker role that exposes these subsystems using a single WebAPI.
Additionally we have one Web Role hosting the web frontend and one Worker Role processing a background queue.
We strive to move to a micro services architecture. The first thing I planned to do was to extract all bounded context into their own API-hosts. This will result in 5-10 new WebAPI services supporting our subsystems.
To my question, should all of these subsystem/bounded context/API-hosts be their own Service Fabric Application or a service within a single Service Fabric Application?
I've read the documentation, found here Service Fabric Application Model, over and over and I can't figure out where my services fits in.
We want the system to support different versions of the services, and the services should also be possible to scale different from another. There might even be a requirement to have one micro service to run in a larger VM size then the rest.
Please can someone guide me in which suits my needs.
I think you have the right idea, in general terms, that each bounded context is a (micro) service. Service Fabric gives you two levels of organization with applications and services, where an application is a logical grouping of services. Here's what that means for you:
Logically speaking, think of an application as a cohesive set of functionality. The services that collectively form that cohesive set of functionality should be grouped as an application. You can ask yourself, for each service: "does it make sense to deploy this service by itself without these other services?" If the answer is no, then they should probably be grouped in the same application.
Developmentally speaking, the Visual Studio tooling is geared a bit more toward multiple services in one application, but you can have multiple applications in one solution too.
Operationally speaking, an application represents a process boundary, upgrade group, and versioning group:
Each instance of an application you create gets its own process (or set of processes if you have multiple service types in the application). Service instances of a service type share host processes. Service instances of different service types get their own process per type.
The application is the top level upgrade unit, that is, every upgrade you do is an application upgrade. You can upgrade individual services within an application (you don't always have to upgrade every service within an application), but each time you do an upgrade, the application version changes.
You can create side-by-side instances of different versions of the same application type in your cluster. You cannot create side-by-side instances of different versions of the same service type within an application instance.
Placement and scale is done at the service. So for example, you can scale one service in an application, and you can place another service on a larger VM.
Related
As I understand there is no concept of update domain in App Services (and in other PaaS offerings). I am wondering how Azure is handling OS updates if I have only a single instance of an App Service app. Do I need to plan for two and more instances if I want to avoid such cases when an app goes down during the OS/other updates or this is handled without downtime? According to docs App Service has 99.95% SLA - is this time reserved here?
First of all, welcome to the community.
Your application will not become unavailable when App Services is patching the OS, you don't have to worry about that. Imagine if that would be the case, it would be a huge problem. Instead, the PaaS service will make sure your application is replicated to an updated worker node before that happens.
But you should have multiple instances, as a best practice listed in this article:
To avoid a single point-of-failure, run your app with at least 2-3 instances.
Running more than one instance ensures that your application is available when App Service moves or upgrades the underlying VM instances
Have a look at this detailed blog post:
https://azure.github.io/AppService/2018/01/18/Demystifying-the-magic-behind-App-Service-OS-updates.html
When the update reaches a specific region, we update available instances without apps on them, then move the apps to the updated instances, then update the offloaded instances.
The SLA is the same regardless the number of instances, even if you select "1 instance":
We guarantee that Apps running in a customer subscription will be available 99.95% of the time
Have a look at Hyper-V and VMWare, it will give you a rough idea on how App Services handle that.
If you're looking for zero-downtime deployments with App Services, what you are looking for are deployment slots.
Managing versions can be confusing, take a look at this issue I opened, it gives you a detailed how-to approach about managing different slot versions, which is not clearly described by Microsoft docs.
I’m designing my service fabric cluster. I’m between creating one app and hosting all the services inside vs creating 1 app per service.
I didnt find clear guidelines on this. The main advantage I see for 1 app per service is that we can deploy each service independently since it has its own app. We can also host the code in different repos. Are there downsides for this?
A better approach is to have one Application per set of services where the services provide a cohesive function. An Application should be an umbrella for n number of services which are related in their function, for instance they may be within the same bounded context or be related to a common operational unit. However, this doesn't mean they have to be deployed / updated in unison.
Services can be deployed independently within an ApplicationType if you move away from using the DefaultServices construct. You can read about why Default Services should be avoided in Production here - essentially they create a rigid deployment strategy and you lose some of the power of Service Fabric parameterization available via PowerShell.
The concept of an Application may seem at odds with a Microservice architecture, but remember its just a logical grouping, single services within an Application are still independently deployable.
Lots of useful info in the Application Model docs.
The main advantage I see for 1 app per service is that we can deploy each service independently since it has its own app.
You can also deploy\upgrade individual services in same application without affecting the other deployed services. Please check about differential packaging here and here
We can also host the code in different repos
Generally when we split our code into separate repositories is because we have a domain boundary that we don't want to track with other services, for example, services owned by different teams or deployed on different schedule, in this case would make sense to have them as separate applications.
Are there downsides for this?
Technically, no. But there are some possible points you have to keep in mind.
When we talk about Microservices we see them as independent services running on their own with as few dependency as possible on other services, when we talk about applications we kinda go against this 'law', because we have to deploy them together, we shouldn't see applications that way, because the applications is just a logical isolation for these services, so where is the benefit on SF applications?
When you have multiple services deployed (dependent or not on each other), you need a way to keep track of them as a bigger unit, otherwise you might end with:
a cluster full of services that sometimes are not required anymore, and is just there because we 'might be using them' or someone forgot to remove when their peers got obsolete.
Dependent services missing on new deployments
Version of services not compatible with each other (contracts, APIs, and so on)
SF Applications works like a snapshot of these services, so for example, whenever a new service get updated, you also upgrade the application to reference the new definition of your services and their dependencies, this will tell SF "this is how I want my services running" and SF will manage to get them exactly as you described. Does not mean you have to update all of them when a upgrade is required, SF will do if you have to, but you can update just the ones that changed, and them deploy a version of your application that SF will manage the version of each service for you. An analogy, it is like a docker compose file where you specify the containers you have to deploy as a single deployment.
Given that, when you opt out of application concept, you loose these benefits, because now you have to manage every single service on their own and keep track of the versions they depend on, and in cases where two services on different applications need to be deployed together (because of breaking changes for example) you would not be able to easily rollback if one of them fail, because they are not dependent on each other anymore, so you would have to write your own logic to handle this.
A typical scenario you might find yourself in is where a new version of a service get updated and others not updated on same release might stop working, but for your deployment, the new service looks OK, without any error.
So, at the end, is just a trade off, you opt for more flexibility deploying your service, but end up with more maintenance.
I went over this blog Azure SF vs Docker but it didn't answer my doubts completely.
I have Docker Data Center on-prem and i want to push Azure SF into this. But i feel DDC is doing exactly same thing as Service Fabric.
Few things from my mind.
DDC takes care of scaling up, all types of container orchestration, health monitoring etc.
Few items which it doesn't provide :
Service remoting between services, publish subscribe model between services, stateful layer(i've heard about portworx volume rep)
Can someone enlighten me more on when should i go with SF which DDC doesn't provide.
If your application landscape consists of containers and there is no intention to change that then you should probably stick to DDC.
Service Fabric (ASF) has a lot more to offer than support for containers. In fact, in earlier days it did not even had support for containers.
The focus of AFS is to provide a platform for building microservices based applications using stateless services, stateful services and actors.
Things that DDC does not provide:
Stateful Services
Actor model
Stateful Services: The benefit of stateful services is that the data lives where the code lives, so no more separate data stores like a NoSQL or relational database. A great benefit is the reduced latency. So in other words, if you have a frontend running in a container that connects to a container that contains a MySQL server for example, you can replace that using a mix of stateless and stateful services.
Actor model: The actor pattern is a computational model for concurrent or distributed systems in which a large number of these actors can execute simultaneously and independently of each other.
In some scenario's the use of containers in ASF is a temporarily one, to lift and shift existing software and combine that with ASF own service models. In later stages the containers can be replaced by ASF services.
The official docs does list some scenario's as when to run containers on ASF:
IIS lift and shift: If you have existing ASP.NET MVC apps that you want to continue to use, put them in a container instead of migrating them to ASP.NET Core. These ASP.NET MVC apps depend on Internet Information Services (IIS). You can package these applications into container images from the precreated IIS image and deploy them with Service Fabric. See Container Images on Windows Server for information about Windows containers.
Mix containers and Service Fabric microservices: Use an existing container image for part of your application. For example, you might use the NGINX container for the web front end of your application and stateful services for the more intensive back-end computation.
Reduce impact of "noisy neighbors" services: You can use the resource governance ability of containers to restrict the resources that a service uses on a host. If services might consume many resources and affect the performance of others (such as a long-running, query-like operation), consider putting these services into containers that have resource governance.
By the way, in your referenced Q & A the fact that is a Microsoft product is listened as a possible disadvantage. It might still be to some, but Microsoft has announces it will open source ASF.
What is the reasoning behind Applications concept in Service Fabric? What is the recommended relation between Applications and Services? In which scenarios do Applications prove useful?
Here is a nice summary how logical services differ from physical services: https://learn.microsoft.com/en-us/dotnet/standard/microservices-architecture/architect-microservice-container-applications/logical-versus-physical-architecture
Now, in relation to Service Fabric, Service Fabric applications represent logical services while Service Fabric services represent physical services. To simplify it, a Service Fabric application is a deployment unit, so you would put there multiple services that rely on the same persistent storage or have other inter-dependencies so that you really need to deploy them together. If you have totally independent services, you would put them into different Service Fabric applications.
An application is a collection of constituent services that perform a certain function or functions. A service performs a complete and standalone function and can start and run independently of other services. A service is composed of code, configuration, and data. For each service, code consists of the executable binaries, configuration consists of service settings that can be loaded at run time, and data consists of arbitrary static data to be consumed by the service. Each component in this hierarchical application model can be versioned and upgraded independently.
It is described here in detail
How I currently see it, applications are a nice concept to group multiple services together and manage them as single unit. In context of service fabric, this is useful if you have multiple nano-services which do not warrant them being completely standalone; instead you can package them together into microservices (SF application).
Disclaimers:
- nano-service would be a REALLY small piece of code running as a stateless SF service for example (e.g. read from queue, couple of lines of code to process, write to another queue).
- in case of "normal" microservices, one could consider packaging them as 1 SF application = 1 SF service
An application is a required top level container for services. You deploy applications, not services. So you cannot really speak about differences between the two since you cannot have services without an application.
From https://learn.microsoft.com/en-us/azure/service-fabric/service-fabric-application-model:
An application is a collection of constituent services that perform a certain function or functions. A service performs a complete and standalone function (it can start and run independently of other services) and is composed of code, configuration, and data. For each service, code consists of the executable binaries, configuration consists of service settings that can be loaded at run time, and data consists of arbitrary static data to be consumed by the service. Each component in this hierarchical application model can be versioned and upgraded independently.
Take a look at the link provided and you will see the hierarchical relationship.
What is established best practice in porting a Windows Service to Azure? Should it be changed into a Worker Role or moved into a VM Role? Are there other options? Assume that my services write to external persistence sources (MSMQ, databases, WCF) rather than to the file system directly.
You are far better off converting your Windows Services to Worker-Roles than VM roles. VM roles are meant to house applications that require complex un-automatable installation procedures. They are also a bigger pain to manage and you want to stay away from VM roles as much as possible. If you can find a way to automate deployment of your existing Windows Services via Worker-Roles, it is definitely the way to go.
You can also looking into HPC roles and depending on the on-prem/off-prem and load/compute requirements, adding Azure machines to your HPC cluster maybe of benefit.
All types of Roles (Web/Worker/VM/HPC) are stateless and require to be able to spin-up or tear-down from scratch on demand. All types of Roles are meant to run more than one VM instance at a time.
HTH
I wrote a blog post about this a while back. It is here:
http://blogs.msdn.com/b/golive/archive/2011/02/11/installing-a-windows-service-in-a-worker-role.aspx
Note that a Windows Service won't communicate directly with the fabric controller, so you need to ping it periodically to check health, then take remediative actions as needed.
Putting a Windows Service into a worker or web role is accepted practice. The main reason to go with VM Role is if there is significant (>10 minutes) setup required. My blog post details how to install your service.
Of course, if you want to move the code into a worker role, that's also fine. In this case you don't need any special steps to ensure the fabric controller is aware of its health.
If cost is an issue, combining functions into web/worker is also accepted practice. And you can save by not working over your code to get it into a web/worker.
Azure has a special type of Web Role called "WCF Service Web Role" which corresponds to a Windows WCF Service. This is a good point for migrating existing services.
Ideally the migration should be followed by taking advantage of Azure specific features, for instance using queues and work roles to maximise perfromance and scalability.