I am new at Kubernetes and am trying to understand the most efficient and secure way to handle sensitive persisted data that interacts with a k8 pod. I have the following requirements when I start a pod in a k8s cluster:
The pod should have persisted storage.
Data inside the pod should be persistent even if the pod crashes or restarts.
I should be able to easily add or remove data from hostPath into the pod. (Not sure if this is feasible since I do not know how the data will behave if the pod starts on a new node in a multi node environment. Do all nodes have access to the data on the same hostPath?)
Currently, I have been using StatefulSets with a persistent volume claim on GKE. The image that I am using has a couple of constraints as follows:
I have to mount a configuration file into the pod before it starts. (I am currently using configmaps to pass the configuration file)
The pod that comes up, creates its own TLS certificates which I need to pass to other pods. (Currently I do not have a process in place to do this and thus have been manually copy pasting these certificates into other pods)
So, how do I maintain a common persisted storage that handles sensitive data between multiple pods and how do I add pre-configured data to this storage? Any guidance or suggestions are appreciated.
I believe this documentation on creating a persistent disk with multiple readers [1] is what you are looking for. you will however only be able to have the pods read from the disk since GCP does not support "WRITEMANY".
Regarding hostpaths, the mount point is on the pod the volume is a directory on the node. I believe the hostpath is confined to individual nodes.
[1] https://cloud.google.com/kubernetes-engine/docs/how-to/persistent-volumes/readonlymany-disks
[2] https://kubernetes.io/docs/concepts/storage/persistent-volumes/#access-modes
Related
To use storage inside Kubernetes PODs I can use volumes and persistent volumes. While the volumes like emptyDir are ephemeral, I could use hostPath and many other cloud based volume plugins which would provide a persistent solution in volumes itself.
In that case why should I be using Persistent Volume then?
It is very important to understand the main differences between Volumes and PersistentVolumes. Both Volumes and PersistentVolumes are Kubernetes resources which provides an abstraction of a data storage facility.
Volumes: let your pod write to a filesystem that exists as long as the pod exists. They also let you share data between containers in the same pod but data in that volume will be destroyed when the pod is restarted. Volume decouples the storage from the Container. Its lifecycle is coupled to a pod.
PersistentVolumes: serves as a long-term storage in your Kubernetes cluster. They exist beyond containers, pods, and nodes. A pod uses a persistent volume claim to to get read and write access to the persistent volume. PersistentVolume decouples the storage from the Pod. Its lifecycle is independent. It enables safe pod restarts and sharing data between pods.
When it comes to hostPath:
A hostPath volume mounts a file or directory from the host node's
filesystem into your Pod.
hostPath has its usage scenarios but in general it might not recommended due to several reasons:
Pods with identical configuration (such as created from a PodTemplate) may behave differently on different nodes due to different files on the nodes
The files or directories created on the underlying hosts are only writable by root. You either need to run your process as root in a privileged Container or modify the file permissions on the host to be able to write to a hostPath volume
You don't always directly control which node your pods will run on, so you're not guaranteed that the pod will actually be scheduled on the node that has the data volume.
If a node goes down you need the pod to be scheduled on other node where your locally provisioned volume will not be available.
The hostPath would be good if for example you would like to use it for log collector running in a DaemonSet.
I recommend the Kubernetes Volumes Guide as a nice supplement to this topic.
PersistentVoluemes is cluster-wide storage and allows you to manage the storage more centrally.
When you configure a volume (either using hostPath or any of the cloud-based volume plugins) then you need to do this configuration within the POD definition file. Every configuration information, required to configure storage for the volume, goes within the POD definition file.
When you have a large environment with a lot of users and a large number of PODs then users will have to configure storage every time for each POD they deploy. Whatever storage solution is used, the user who deploys the POD will have to configure that storage on all of his/her POD definition files. If a change needs to be made then the user will have to make this change on all of his/her PODs. After a certain scale, this is not the most optimal way to manage storage.
Instead, you would like to manage this centrally. You would like to manage the storage in such a way that an Administrator can create a large pool of storage and users can carve out a part of this storage as required, and this is exactly what you can do using PersistentVolumes and PersistentVolumeClaims.
Use PersistentVolumes when you need to set up a database like MongoDB, Redis, Postgres & MySQL. Because it's long-term storage and not deeply coupled with your pods! Perfect for database applications. Because they will not die with the pods.
Avoid Volumes when you need long-term storage. Because they will die with the pods!
In my case, when I have to store something, I will always go for persistent volumes!
According to the documentation:
A PersistentVolume (PV) is a piece of storage in the cluster that has been provisioned ... It is a resource in the cluster just like a node is a cluster resource...
So I was reading about all currently available plugins for PVs and I understand that for 3rd-party / out-of-cluster storage this doesn't matter (e.g. storing data in EBS, Azure or GCE disks) because there are no or very little implications when adding or removing nodes from a cluster. However, there are different ones such as (ignoring hostPath as that works only for single-node clusters):
csi
local
which (at least from what I've read in the docs) don't require 3rd-party vendors/software.
But also:
... local volumes are subject to the availability of the underlying node and are not suitable for all applications. If a node becomes unhealthy, then the local volume becomes inaccessible by the pod. The pod using this volume is unable to run. Applications using local volumes must be able to tolerate this reduced availability, as well as potential data loss, depending on the durability characteristics of the underlying disk.
The local PersistentVolume requires manual cleanup and deletion by the user if the external static provisioner is not used to manage the volume lifecycle.
Use-case
Let's say I have a single-node cluster with a single local PV and I want to add a new node to the cluster, so I have 2-node cluster (small numbers for simplicity).
Will the data from an already existing local PV be 1:1 replicated into the new node as in having one PV with 2 nodes of redundancy or is it strictly bound to the existing node only?
If the already existing PV can't be adjusted from 1 to 2 nodes, can a new PV (created from scratch) be created so it's 1:1 replicated between 2+ nodes on the cluster?
Alternatively if not, what would be the correct approach without using a 3rd-party out-of-cluster solution? Will using csi cause any change to the overall approach or is it the same with redundancy, just different "engine" under the hood?
Can a new PV be created so it's 1:1 replicated between 2+ nodes on the cluster?
None of the standard volume types are replicated at all. If you can use a volume type that supports ReadWriteMany access (most readily NFS) then multiple pods can use it simultaneously, but you would have to run the matching NFS server.
Of the volume types you reference:
hostPath is a directory on the node the pod happens to be running on. It's not a directory on any specific node, so if the pod gets recreated on a different node, it will refer to the same directory but on the new node, presumably with different content. Aside from basic test scenarios I'm not sure when a hostPath PersistentVolume would be useful.
local is a directory on a specific node, or at least following a node-affinity constraint. Kubernetes knows that not all storage can be mounted on every node, so this automatically constrains the pod to run on the node that has the directory (assuming the node still exists).
csi is an extremely generic extension mechanism, so that you can run storage drivers that aren't on the list you link to. There are some features that might be better supported by the CSI version of a storage backend than the in-tree version. (I'm familiar with AWS: the EBS CSI driver supports snapshots and resizing; the EFS CSI driver can dynamically provision NFS directories.)
In the specific case of a local test cluster (say, using kind) using a local volume will constrain pods to run on the node that has the data, which is more robust than using a hostPath volume. It won't replicate the data, though, so if the node with the data is deleted, the data goes away with it.
I'm running a k3s single node cluster and have the k3s local-path-provisioner as storage. As I want to be able to add nodes in the future, I looked at minio to use on top of the local-path as storage. But I'm not sure if it's the right choice, cause I my workloads primarily use mariadb for data and I read, that an s3 compatible bucket isn't the best for database applications.
I hope you can help me figure this out.
If you don't want to use object storage then here are your options for running a local storage provisioner:
GlusterFS StorageClass
Doesn't have lot of documentation on how to set it up. But if you know your way around GlusterFS It'll be a good option.
local-path-provisioner
I
t provides a way for the Kubernetes users to utilize the local storage in each node
OpenEBS -> has a local volume storage engine but I think this is not designed to work on a shared volume mount and it end up tying a pod to a specific node since the data "doesn't exist" on the other nodes.
longhorn [recommened]
It creates a dedicated storage controller for each block device volume and synchronously replicates the volume across multiple replicas stored on multiple nodes.
rook
Rook is a storage operators for Kubernetes, It supports multiple storage backends. Don't use the NFS one tho cause we hit a wall when using it with our DBs.
We have started setting up a Kubernetes cluster. On Production, we have 4 Mysql Nodes(2 Active Master, 2 Active slaves). Complete servers are on-premise, There is NO cloud providers usage.
Now how do I configure storage? I mean should I use PV / PVC? How will it work. Should I use local PV? Can someone explain to me this?
You need to use PersistentVolumes and PersistentVolumeClaims in order to achieve that.
A PersistentVolume (PV) is a piece of storage in the cluster that has
been provisioned by an administrator or dynamically provisioned using
Storage Classes.
A PersistentVolumeClaim (PVC) is a request for storage by a user.
Claims can request specific size and access modes (e.g., they can be
mounted once read/write or many times read-only).
Containers are ephemeral. When the container is restarted all the changes made prior to it are lost. Databases, however expect the data is persistent, therefore you need persistent volumes. You have to create a storage claim and the pod must be configured to mount the claimed storage.
Here you will find a simple guide showing how to deploy MySQL with a PersistentVolume. However, I strongly recommend getting familiar with the official docs that I have linked in order to fully understand the concept and adjust the access mode, class, size, etc according to your needs.
Please let me know if that helped.
When we deploy apache kafka on Linux/Windows, we have log.dirs and broker.id properties. on bare metal, the files are saved on the individual host instances. However, when deployed via K8s on public cloud - there must be some form of volume mounting to make sure that the transaction log fils are saved somewhere?
Has anyone done this on K8s? I am not referring to Confluent (because it's a paid subscription).
As far as I understand you are just asking how to deal with storage in Kubernetes.
Here is a great clip that talks about Kubernetes Storage that I would recommend to You.
In Kubernetes you are using Volumes
On-disk files in a Container are ephemeral, which presents some problems for non-trivial applications when running in Containers. First, when a Container crashes, kubelet will restart it, but the files will be lost - the Container starts with a clean state. Second, when running Containers together in a Pod it is often necessary to share files between those Containers. The Kubernetes Volume abstraction solves both of these problems.
There is many types of Volumes, some are cloud specific like awsElasticBlockStore, gcePersistentDisk, azureDisk and azureFile.
There are also other types like glusterfs, iscsi, nfs and many more that are listed here.
You can also use Persistent Volumes which provides an API for users and administrators that abstracts details of how storage is provided from how it is consumed:
A PersistentVolume (PV) is a piece of storage in the cluster that has been provisioned by an administrator. It is a resource in the cluster just like a node is a cluster resource. PVs are volume plugins like Volumes, but have a lifecycle independent of any individual pod that uses the PV. This API object captures the details of the implementation of the storage, be that NFS, iSCSI, or a cloud-provider-specific storage system.
A PersistentVolumeClaim (PVC) is a request for storage by a user. It is similar to a pod. Pods consume node resources and PVCs consume PV resources. Pods can request specific levels of resources (CPU and Memory). Claims can request specific size and access modes (e.g., can be mounted once read/write or many times read-only).
Here is a link to Portworx Kafka Kubernetes in production: How to Run HA Kafka on Amazon EKS, GKE and AKS which might be handy for you as well.
And if you would be interested in performance then Kubernetes Storage Performance Comparison is a great 10min read.
I hope those materials will help you understand Kubernetes storage.