Our cloud application consists of 3 tightly coupled Docker containers, Nginx, Web and Mongo. Currently we run these containers on a single machine. However as our users are increasing we are looking for a solution to scale. Using Kubernetes we would form a multi container pod. If we are to replicate we need to replicate all 3 containers as a unit. Our cloud application is consumed by mobile app users. Our app can only handle approx 30000 users per Worker node and we intend to place a single pod on a single worker node. Once a mobile device is connected to worker node it must continue to only use that machine ( unique IP address )
We plan on using Kubernetes to manage the containers. Load balancing doesn't work for our use case as a mobile device needs to be tied to a single machine once assigned and each Pod works independently with its own persistent volume. However we need a way of spinning up new Pods on worker nodes if the number of users goes over 30000 and so on.
The idea is we have some sort of custom scheduler which assigns a mobile device a Worker Node ( domain/ IPaddress) depending on the number of users on that node.
Is Kubernetes a good fit for this design and how could we implement a custom pod scale algorithm.
Thanks
Piggy-Backing on the answer of Jonah Benton:
While this is technically possible - your problem is not with Kubernetes it's with your Application! Let me point you the problem:
Our cloud application consists of 3 tightly coupled Docker containers, Nginx, Web, and Mongo.
Here is your first problem: Is you can only deploy these three containers together and not independently - you cannot scale one or the other!
While MongoDB can be scaled to insane loads - if it's bundled with your web server and web application it won't be able to...
So the first step for you is to break up these three components so they can be managed independently of each other. Next:
Currently we run these containers on a single machine.
While not strictly a problem - I have serious doubt's what it would mean to scale your application and what the challenges that come with scalability!
Once a mobile device is connected to worker node it must continue to only use that machine ( unique IP address )
Now, this IS a problem. You're looking to run an application on Kubernetes but I do not think you understand the consequences of doing that: Kubernetes orchestrates your resources. This means it will move pods (by killing and recreating) between nodes (and if necessary to the same node). It does this fully autonomous (which is awesome and gives you a good night sleep) If you're relying on clients sticking to a single nodes IP, you're going to get up in the middle of the night because Kubernetes tried to correct for a node failure and moved your pod which is now gone and your users can't connect anymore. You need to leverage the load-balancing features (services) in Kubernetes. Only they are able to handle the dynamic changes that happen in Kubernetes clusters.
Using Kubernetes we would form a multi container pod.
And we have another winner - No! You're trying to treat Kubernetes as if it were your on-premise infrastructure! If you keep doing so you're going to fail and curse Kubernetes in the process!
Now that I told you some of the things you're thinking wrong - what a person would I be if I did not offer some advice on how to make this work:
In Kubernetes your three applications should not run in one pod! They should run in separate pods:
your webservers work should be done by Ingress and since you're already familiar with nginx, this is probably the ingress you are looking for!
Your web application should be a simple Deployment and be exposed to ingress through a Service
your database should be a separate deployment which you can either do manually through a statefullset or (more advanced) through an operator and also exposed to the web application trough a Service
Feel free to ask if you have any more questions!
Building a custom scheduler and running multiple schedulers at the same time is supported:
https://kubernetes.io/docs/tasks/administer-cluster/configure-multiple-schedulers/
That said, to the question of whether kubernetes is a good fit for this design- my answer is: not really.
K8s can be difficult to operate, with the payoff being the level of automation and resiliency that it provides out of the box for whole classes of workloads.
This workload is not one of those. In order to gain any benefit you would have to write a scheduler to handle the edge failure and error cases this application has (what happens when you lose a node for a short period of time...) in a way that makes sense for k8s. And you would have to come up to speed with normal k8s operations.
With the information provided, hard pressed to see why one would use k8s for this workload over just running docker on some VMs and scripting some of the automation.
Related
Right now I am struggling with debugging of NodeJs application which is clustered and is running on Docker. Found on this link and this information in it:
Remember, Node.js is still single-threaded in most cases, so even on a
single server you’ll likely want to spin up multiple container
replicas to take advantage of multiple CPU’s
So what does it mean, clustering of NodeJs app is pointless when it is meant to be deployed on Kubernetes ?
EDIT: I should also say that, by clustering I mean forking workers with cluster.fork() and goal of the application is to build simple REST API with high load traffic.
Short answer is yes..
Containers are just mini VM's and kubernetes is the orchestration tool that manages all the running 'containers', checking for health, resource allocation, load etc.
So, if you are running your node application in a container with an orchestration tool like kubernetes, then clustering is moot as each 'container' will be using 1 CPU or partial CPU depending on how you have it configured. Multiple containers essentially just place a new VM in rotation and kubernetes will direct traffic to each.
Now, when we talk about clustering node, that really comes into play when using tools like PM2, lets say you have a beefy server with 8 CPU's, node can only use 1 per instance so tools like PM2 setup a cluster and will route traffic along each of the running instances.
One thing to keep in mind though is that your application needs to be cluster OR container ready. Meaning nothing should be stored on the ephemeral disk as with each container restart that data is lost OR in a cluster situation there is no guarantee the folders will be available to each running instance and if you cluster with multiple servers etc you are asking for trouble :D ( this is where an object store would come into play like S3)
I'm currently rethinking an architecture I was planning.
So suppose I have a system where there are about 8 different services interacting with a single database. Some services listen and react to database events and do stuff like sending SMS.
Then there's an API layer sitting on top of the database and a frontend connected to this API. So in my understanding this is rather monolithic.
In fact I don't see any advantage of using containers in this scenario. Their real advantage is that they can be swapped out, right? My intuition tells me that there is often no purpose in doing that except maybe some load balancing on API level. Instead many companies just seem to blindly jump on the hype train of containerizing everything.
Now the question arises, is docker the right tool for this context? In each forum people refrain from using docker for the sole purpose of a more resource efficient "VM" aggregating all services within a single container. However this is the only real scenario I'd see any advantages in using docker (the environment, e.g. alpine-linux, is the same on all customer's computers when rolling out the system).
Even docker-compose is not "grouping" containers together as a complete system only exposing port 443 but instead starts an infrastructure of multiple interacting containers. Oftentimes services like Kubernetes are then used for deploying these infrastructures on "nodes", i.e. VMs.
However, in my opinion it would be great to have a single self-contained container without putting them into a VM. This container would include every necessary service only exposing one port, e.g. 443.
Since I'm rather confused now, I'd really appreciate your help here.
Thanks in advance!
Kubernetes does many things and has many useful features. But Kubernetes also require that you architect your apps to follow The Twelve-Factor App principles. An important thing here is that your apps are stateless.
When the app is stateless, it is easy to scale out horizontally - this can also be done automatically when the load increases.
When the app is stateless, it is easy to do Rolling Deployments that upgrade the app to a new version without downtime.
You can run containers on bare metal Linux servers, but this is mostly very big servers. If you use a cloud, you probably want more VM instances, but distributed to 3 Availability Zones - for increased availability.
"Self-contained container - exposing one port". With Kubernetes, you typically use a private network and you only expose services via a single load balancer - typically on a port, but different URLs send traffic to different services.
Some services listen and react to database events and do stuff like sending SMS.
As I said, many things is easier when it is horizontal scalable, but this kind of app - that listen for events and react - is one of few examples where you can not scale horizontally. But it is a good fit for a serverless architecture instead, possibly on Kubernetes using Knative.
Now the question arises, is docker the right tool for this context?
My opinion is that most workload will run in containers. It is more a question about how it should be run in Kubernetes - one or multiple replicas. As stateless Deployments or stateful StatefulSet or some other way.
I recently finished a project where I created an App consisting of several docker containers. The purpose of the app was to collect some data and safe it to an databank and also allow user interactions over an simple web gui. The app was hosted on four different Raspberry Pi's and it was possible to collect data from all physicial maschines through an api. Further you could do some simple machine learning tasks like calculating anomalies in the sensor data of the Pi's.
Now I'm trying to take the next step and using kubernetes for some load balancing and remote updates. My main goal is to remote update all raspberries from my master node. Which, in theory, would be a very handy feature. Also I want to share the ressources of the Pi's within the cluster for calculations.
I read a lot about Kubernets, Minikube, K3's, Kind and all the different approaches to set up an Kubernetes cluster, but feel like I am missing "a last puzzle piece".
So from what I understood I need an approach which allows me to set up an local (because all machines are laying on my desk/ no cloud needed) multi node cluster. My master node would be (idealy) my laptop, running Ubuntu in a virtual machine. My rasberry's would be my slave/worker nodes. If I would want to update my cluster I can use the kubernetes remote update functionality.
So my question out of this would be: Does it makes sense to use several rasberries as nodes in a kubernetes cluster and to manage them from one master node (laptop) and do you have any suggestions about the way to achieve this setup.
I usally dont like those question not containing any specific code or questions by myself, but feel like an simple hint could accelerate my project noteable. If it's the wrong place please feel free to delete this question.
Best regards
You didn't mention which rpi models you are using, but I assume you are not using rpi zeros.
My main goal is to remote update all raspberries from my master node.
Assuming that by that you mean updating your applications running in kubernetes that is installed on rpi then keep reading. Otherwise ignore all I wrote, and what you probably need is ansible or other simmilar provisioning/configuration-management/application-deployment tool.
Now answering to your question:
Does it makes sense to use several rasberries as nodes in a kubernetes cluster
yes, this is why people created k3s, so such setup is possible using less resources.
and to manage them from one master node (laptop)
assuming you will be using it for learning purpouses then why not. It is possible, but just be aware that when master node goes down (e.g. when you turn off your laptop), all cluster goes down (or at least api-server communication so you wont be able to change cluster's state). Also make sure you are using bridge networking interface for your VM so it is visible in your local network as a standalone instance.
and do you have any suggestions about the way to achieve this setup.
installing k3s on all nodes would be the easiest in your case. There are plenty of resources on the internet explaining how to achieve it.
One last thing I would like to explain is the thing with updates.
Speaking of kubernetes updates you need to know that kubernetes doesn't update itself automatically. You need to explicitly update it. New k8s version is beeing released every 3 months that sometimes "breaks" things and backward compatibility is not possible (so always read changelog before updating stuff because rollbacks may not be possible unless you backed up an etcd cluster earlier).
Speaking of updating applications - To run your app all you do is send yaml files describing your application to k8s and it handles the rest. So if you want to update your app just update the tag on container image to newer version and k8s will handle the updates. Read here more about update strategies in k8s.
I have been looking into the new Docker Swarm mode that will be available in Docker 1.12. In this Docker Swarm Mode Walkthrough video, they create a simple Nginx service that is composed of a single Nginx container. In the video, they have 4 nodes in the Swarm cluster. During the scaling demonstration, they increase the replication factor to 10, thus creating 10 copies of the Nginx container across all 4 machines in the cluster.
I get that the video is just a demonstration, but in the real world, what is the point of creating more replicas of a container (or service) than there are nodes in the Swarm cluster? It seems to be pointless since two containers on the same machine would be sharing that machines finite computing resources anyway. I don't get what the benefit is.
So my question is, is there any real world benefit to replicating a Docker service or container beyond the number of nodes in the Swarm cluster?
Thanks
It depends on how the application handles threading and multiple requests. A single threaded application, or job that only handles one request at a time, may use a fraction of the OS resources and benefit from running multiple instances on a single host. An application that's been tuned to process requests concurrently and which fully utilizes the OS will see no benefit and will in fact incur a penalty of taking away resources to run multiple instances of the application.
One advantage can be performing live zero-downtime software updates. See the Docker 0.12rc2 Swarm tutorial on rolling updates
You have a RabbitMQ or other Queue System with a high load on data. You can start more Containers with workers than nodes to handle the high data load on your RabbitMQ.
Hardware resource constrain is not the only thing one needs to consider when you have your services replicated.
A simple example would be if you are having a service to provide security details. The resource consumption by this service will be low (read a record from Db/Cache and send it out). However if there are 20 or 30 requests to be handled by the same service the requests will be queued up.
Yes there are better ways to implement my example but I believe is good enough to illustrate why one might replicate a service on the same host/node.
I Have the following setup in mind:
Kubernetes on Mesos (based on the kubernetes-mesos project) within a /16 network.
Each pod will have its own IP and I believe this will avail 64 000 pods.
The idea is to provide isolation for each app i.e. Each app gets its own mysql within the same pod - the app accesses mysql on localhost(within the pod).
If an additional service were needed, I'd use kubernetes rolling updates to add the service's container to the pod, the app will be able to access this new service on localhost as well.
Each application needs as much isolation as possible.
Are there any defects to such an implementation?
Do I have to use weave?
There's an option to specify the service-ip-range while running the kubernetes-mesos install.
One hole is how do I scale a service, is this really viable?
Is there a better way to do this? i.e. Offering isolated services
Thanks.
PS//I'm obviously a noobie at this and I'm trying to get the best possible setup running.
A common misconception is that a Pod should manage a vertical, multi-tier stack: for example a web tier + DB tier together.
It's interesting to read the Kubernetes design intent of Pods: they're for collecting 'helper' processes rather than composing a vertical stack.
To answer your questions, I'd recommend:
Define a Pod template for the web tier only. This can be scaled to any size required, using a replication controller (questions #1 and #3).
Define another Pod for MySQL.
Use the Service abstraction to locate these components.
This sort of design will work for small applications, but you're right that it'll be tough to scale up if you suddenly want two have a couple instances of a service hit the same mysql backend.
You may want to look into putting each service into a separate namespace. Then a service's DNS lookups will be scoped to its own namespace by default so that it won't find other services' resources unless it's explicitly looking for them. This would let you put mysql (and any other dependencies) in a separate pod so that the frontend could be scaled independently.