In this chapter, we will implement the ability to download and upload files in the application. In addition, we will discuss some aspects of working with files in Kubernetes and provide a practical example of using S3-compatible storage.
The application described in this chapter is not intended for use in production environments as-is. Note that successful completion of this entire guide is required to create a production-ready application.
Preparing the environment
If you haven’t prepared your environment during previous steps, please, do it using the instructions provided in the “Preparing the environment” chapter.
If your environment has stopped working or instructions in this chapter don’t work, please, refer to these hints:
Let’s launch Docker Desktop. It takes some time for this application to start Docker. If there are no errors during the startup process, check that Docker is running and is properly configured:
docker run hello-world
You will see the following output if the command completes successfully:
Unable to find image 'hello-world:latest' locally
latest: Pulling from library/hello-world
b8dfde127a29: Pull complete
Digest: sha256:9f6ad537c5132bcce57f7a0a20e317228d382c3cd61edae14650eec68b2b345c
Status: Downloaded newer image for hello-world:latest
Hello from Docker!
This message shows that your installation appears to be working correctly.
Should you have any problems, please refer to the Docker documentation.
Let’s launch the Docker Desktop application. It takes some time for the application to start Docker. If there are no errors during the startup process, then check that Docker is running and is properly configured:
docker run hello-world
You will see the following output if the command completes successfully:
Unable to find image 'hello-world:latest' locally
latest: Pulling from library/hello-world
b8dfde127a29: Pull complete
Digest: sha256:9f6ad537c5132bcce57f7a0a20e317228d382c3cd61edae14650eec68b2b345c
Status: Downloaded newer image for hello-world:latest
Hello from Docker!
This message shows that your installation appears to be working correctly.
Should you have any problems, please refer to the Docker documentation.
Start Docker:
sudo systemctl restart docker
Make sure that Docker is running:
sudo systemctl status docker
If the Docker start is successful, you will see the following output:
● docker.service - Docker Application Container Engine
Loaded: loaded (/lib/systemd/system/docker.service; enabled; vendor preset: enabled)
Active: active (running) since Thu 2021-06-24 13:05:17 MSK; 13s ago
TriggeredBy: ● docker.socket
Docs: https://docs.docker.com
Main PID: 2013888 (dockerd)
Tasks: 36
Memory: 100.3M
CGroup: /system.slice/docker.service
└─2013888 /usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock
dockerd[2013888]: time="2021-06-24T13:05:16.936197880+03:00" level=warning msg="Your kernel does not support CPU realtime scheduler"
dockerd[2013888]: time="2021-06-24T13:05:16.936219851+03:00" level=warning msg="Your kernel does not support cgroup blkio weight"
dockerd[2013888]: time="2021-06-24T13:05:16.936224976+03:00" level=warning msg="Your kernel does not support cgroup blkio weight_device"
dockerd[2013888]: time="2021-06-24T13:05:16.936311001+03:00" level=info msg="Loading containers: start."
dockerd[2013888]: time="2021-06-24T13:05:17.119938367+03:00" level=info msg="Loading containers: done."
dockerd[2013888]: time="2021-06-24T13:05:17.134054120+03:00" level=info msg="Daemon has completed initialization"
systemd[1]: Started Docker Application Container Engine.
dockerd[2013888]: time="2021-06-24T13:05:17.148493957+03:00" level=info msg="API listen on /run/docker.sock"
Now let’s check if Docker is available and its configuration is correct:
docker run hello-world
You will see the following output if the command completes successfully:
Unable to find image 'hello-world:latest' locally
latest: Pulling from library/hello-world
b8dfde127a29: Pull complete
Digest: sha256:9f6ad537c5132bcce57f7a0a20e317228d382c3cd61edae14650eec68b2b345c
Status: Downloaded newer image for hello-world:latest
Hello from Docker!
This message shows that your installation appears to be working correctly.
Should you have any problems, please refer to the Docker documentation.
Let’s start the minikube cluster we have already configured in the “Preparing the environment” chapter:
minikube start
Set the default Namespace so that you don’t have to specify it every time you invoke kubectl:
kubectl config set-context minikube --namespace=werf-guide-app
You will see the following output if the command completes successfully:
😄 minikube v1.20.0 on Ubuntu 20.04
✨ Using the docker driver based on existing profile
👍 Starting control plane node minikube in cluster minikube
🚜 Pulling base image ...
🎉 minikube 1.21.0 is available! Download it: https://github.com/kubernetes/minikube/releases/tag/v1.21.0
💡 To disable this notice, run: 'minikube config set WantUpdateNotification false'
🔄 Restarting existing docker container for "minikube" ...
🐳 Preparing Kubernetes v1.20.2 on Docker 20.10.6 ...
🔎 Verifying Kubernetes components...
▪ Using image gcr.io/google_containers/kube-registry-proxy:0.4
▪ Using image k8s.gcr.io/ingress-nginx/controller:v0.44.0
▪ Using image registry:2.7.1
▪ Using image docker.io/jettech/kube-webhook-certgen:v1.5.1
▪ Using image docker.io/jettech/kube-webhook-certgen:v1.5.1
▪ Using image gcr.io/k8s-minikube/storage-provisioner:v5
🔎 Verifying registry addon...
🔎 Verifying ingress addon...
🌟 Enabled addons: storage-provisioner, registry, default-storageclass, ingress
🏄 Done! kubectl is now configured to use "minikube" cluster and "werf-guide-app" namespace by default
Make sure that the command output contains the following line:
Restarting existing docker container for "minikube"
Its absence means that a new minikube cluster was created instead of using the old one. In this case, repeat all the steps required to install the environment using minikube.
Now run the command in the background PowerShell terminal (do not close its window):
minikube tunnel --cleanup=true
Let’s start the minikube cluster we have already configured in the “Preparing the environment” chapter:
minikube start --namespace werf-guide-app
Set the default Namespace so that you don’t have to specify it every time you invoke kubectl:
kubectl config set-context minikube --namespace=werf-guide-app
You will see the following output if the command completes successfully:
😄 minikube v1.20.0 on Ubuntu 20.04
✨ Using the docker driver based on existing profile
👍 Starting control plane node minikube in cluster minikube
🚜 Pulling base image ...
🎉 minikube 1.21.0 is available! Download it: https://github.com/kubernetes/minikube/releases/tag/v1.21.0
💡 To disable this notice, run: 'minikube config set WantUpdateNotification false'
🔄 Restarting existing docker container for "minikube" ...
🐳 Preparing Kubernetes v1.20.2 on Docker 20.10.6 ...
🔎 Verifying Kubernetes components...
▪ Using image gcr.io/google_containers/kube-registry-proxy:0.4
▪ Using image k8s.gcr.io/ingress-nginx/controller:v0.44.0
▪ Using image registry:2.7.1
▪ Using image docker.io/jettech/kube-webhook-certgen:v1.5.1
▪ Using image docker.io/jettech/kube-webhook-certgen:v1.5.1
▪ Using image gcr.io/k8s-minikube/storage-provisioner:v5
🔎 Verifying registry addon...
🔎 Verifying ingress addon...
🌟 Enabled addons: storage-provisioner, registry, default-storageclass, ingress
🏄 Done! kubectl is now configured to use "minikube" cluster and "werf-guide-app" namespace by default
Make sure that the command output contains the following line:
Restarting existing docker container for "minikube"
Its absence means that a new minikube cluster was created instead of using the old one. In this case, repeat all the steps required to install the environment from scratch using minikube.
If you have inadvertently deleted Namespace of the application, you must run the following commands to proceed with the guide:
kubectl create namespace werf-guide-app
kubectl create secret docker-registry registrysecret \
--docker-server='https://index.docker.io/v1/' \
--docker-username='<Docker Hub username>' \
--docker-password='<Docker Hub password>'
You will see the following output if the command completes successfully:
namespace/werf-guide-app created
secret/registrysecret created
If nothing worked, repeat all the steps described in the “Preparing the environment” chapter and create a new environment from scratch. If creating an environment from scratch did not help either, please, tell us about your problem in our Telegram chat or create an issue on GitHub. We will be happy to help you!
Preparing the repository
Update the existing repository containing the application:
Run the following commands in PowerShell:
cd ~/werf-guide/app
# To see what changes we will make later in this chapter, let's replace all the application files
# in the repository with new, modified files containing the changes described below.
git rm -r .
cp -Recurse -Force ~/werf-guide/guides/examples/django/050_s3/* .
git add .
git commit -m WIP
# Enter the command below to show the files we are going to change.
git show --stat
# Enter the command below to show the changes that will be made.
git show
Run the following commands in Bash:
cd ~/werf-guide/app
# To see what changes we will make later in this chapter, let's replace all the application files
# in the repository with new, modified files containing the changes described below.
git rm -r .
cp -rf ~/werf-guide/guides/examples/django/050_s3/. .
git add .
git commit -m WIP
# Enter the command below to show files we are going to change.
git show --stat
# Enter the command below to show the changes that will be made.
git show
Doesn’t work? Try the instructions on the “I am just starting from this chapter” tab above.
Prepare a new repository with the application:
Run the following commands in PowerShell:
# Clone the example repository to ~/werf-guide/guides (if you have not cloned it yet).
if (-not (Test-Path ~/werf-guide/guides)) {
git clone https://github.com/werf/website $env:HOMEPATH/werf-guide/guides
}
# Copy the (unchanged) application files to ~/werf-guide/app.
rm -Recurse -Force ~/werf-guide/app
cp -Recurse -Force ~/werf-guide/guides/examples/django/040_db ~/werf-guide/app
# Make the ~/werf-guide/app directory a git repository.
cd ~/werf-guide/app
git init
git add .
git commit -m initial
# To see what changes we will make later in this chapter, let's replace all the application files
# in the repository with new, modified files containing the changes described below.
git rm -r .
cp -Recurse -Force ~/werf-guide/guides/examples/django/050_s3/* .
git add .
git commit -m WIP
# Enter the command below to show the files we are going to change.
git show --stat
# Enter the command below to show the changes that will be made.
git show
Run the following commands in Bash:
# Clone the example repository to ~/werf-guide/guides (if you have not cloned it yet).
test -e ~/werf-guide/guides || git clone https://github.com/werf/website ~/werf-guide/guides
# Copy the (unchanged) application files to ~/werf-guide/app.
rm -rf ~/werf-guide/app
cp -rf ~/werf-guide/guides/examples/django/040_db ~/werf-guide/app
# Make the ~/werf-guide/app directory a git repository.
cd ~/werf-guide/app
git init
git add .
git commit -m initial
# To see what changes we will make later in this chapter, let's replace all the application files
# in the repository with new, modified files containing the changes described below.
git rm -r .
cp -rf ~/werf-guide/guides/examples/django/050_s3/. .
git add .
git commit -m WIP
# Enter the command below to show files we are going to change.
git show --stat
# Enter the command below to show the changes that will be made.
git show
Storing files
Containers running in Kubernetes are often created and deleted automatically, e.g., because of Deployment updates. This means that application files cannot be stored on the container file system since those files will be:
- available to a single container/application replica rather than all of them;
- deleted when the container is killed.
Thus, it makes sense to store in the containers only the data you can afford to lose.
By the way, you can set the container file system to read-only. This will improve security and prevent the application from storing data locally.
But what if you need to keep some data? You can use standalone databases for that. For example, NoSQL databases such as object storages are often used for storing regular files. Object stores that provide an Amazon S3-compatible API are especially popular.
Below, we will show you how to store files in S3-compatible storage instead of a local file system. This way, your application can remain stateless and avoid some issues when working in Kubernetes.
Preliminary steps
Django usually takes advantage of the boto3 library to work with S3.
Let’s add it to the project by including the install command in the Dockerfile:
...
RUN python -m pip install Django uwsgi mysqlclient boto3
Adding /upload and /download endpoints to the application
Let’s add two new endpoints, /upload (to upload a file to the S3-compatible object storage) and /download (to download a file from the S3-compatible object storage), to see how uploading and downloading works.
Let’s add a new controller:
from django.http import HttpResponseBadRequest, HttpResponse
from django.shortcuts import render
from .forms import UploadFileForm
from .minio import upload_to_s3, download_from_s3
def upload(request):
if request.method == 'POST':
form = UploadFileForm(request.POST, request.FILES)
if form.is_valid():
upload_to_s3(request.FILES['file'].read())
return HttpResponse('File uploaded.\n')
else:
HttpResponseBadRequest("You forgot to attach a file.\n")
return HttpResponseBadRequest("The request method must be POST.")
def download(request):
return HttpResponse(download_from_s3())
Now it is time to add new paths to the routes:
...
path('upload', storage_view.upload, name='upload'),
path('download', storage_view.download, name='download'),
New endpoints, /upload and /download, have been added. Next, we need to configure them to work with the storage.
Deploying and configuring MinIO
For illustrative purposes, we will use the MinIO S3-compatible object storage. However, you can use any other S3-compatible storage (such as Amazon S3) instead.
If the different type of S3 storage is used, you do not need to create MinIO’s StatefulSet and Job as described below. However, all further steps remain unchanged.
Let’s add a StatefulSet for MinIO:
apiVersion: apps/v1
kind: StatefulSet
metadata:
name: minio
spec:
serviceName: minio
selector:
matchLabels:
app: minio
template:
metadata:
labels:
app: minio
spec:
containers:
- name: minio
image: minio/minio
args: ["server", "/data", "--console-address", ":9001"]
ports:
- containerPort: 9000
name: minio
- containerPort: 9001
name: console
volumeMounts:
- name: minio-data
mountPath: /data
env:
- name: MINIO_ACCESS_KEY
value: "minioadmin"
- name: MINIO_SECRET_KEY
value: "minioadmin"
volumeClaimTemplates:
- metadata:
name: minio-data
spec:
accessModes: ["ReadWriteOnce"]
resources:
requests:
storage: 100Mi
---
apiVersion: v1
kind: Service
metadata:
name: minio
spec:
selector:
app: minio
ports:
- port: 9000
name: minio
- port: 9001
name: console
Add the configuration for connecting to MinIO:
...
env:
- name: MINIO_ENDPOINT
value: "http://minio:9000"
- name: MINIO_ACCESS_KEY
value: "minioadmin"
- name: MINIO_SECRET_KEY
value: "minioadmin"
- name: BUCKET_NAME
value: "werf-guide-app"
- name: MYSQL_DATABASE
value: "django"
- name: MYSQL_HOST
value: "mysql"
- name: MYSQL_USER
value: "django"
- name: MYSQL_PASSWORD
value: "django"
MinIO is now ready to be deployed while our application is configured to store files with it.
Testing the storage
First, let’s deploy our application:
werf converge --repo <DOCKER HUB USERNAME>/werf-guide-app
You should see the following output:
┌ Concurrent builds plan (no more than 5 images at the same time)
│ Set #0:
│ - ⛵ image backend
│ - ⛵ image frontend
└ Concurrent builds plan (no more than 5 images at the same time)
┌ ⛵ image backend
│ Use cache image for backend/dockerfile
│ name: <DOCKER HUB USERNAME>/werf-guide-app:384636338cad8c70b70c4e530032aa930f32b91b8d476aa5cf8219a7-1661359407179
│ id: d9865e6aa43c
│ created: 2022-08-24 19:43:25 +0000 UTC
│ size: 143.3 MiB
└ ⛵ image backend (3.09 seconds)
┌ ⛵ image frontend
│ Use cache image for frontend/dockerfile
│ name: <DOCKER HUB USERNAME>/werf-guide-app:776dd1b11f95e6a08e138ce50ac0c4ece93051b8522db3a905e71e0a-1661341020624
│ id: ef98a01890ab
│ created: 2022-08-24 14:36:58 +0000 UTC
│ size: 9.7 MiB
└ ⛵ image frontend (3.17 seconds)
┌ Waiting for resources to become ready
│ ┌ job/setup-and-migrate-db-rev14 po/setup-and-migrate-db-rev14-k5hhf container/setup-and-migrate-db logs
│ │ Operations to perform:
│ │ Apply all migrations: admin, auth, contenttypes, sessions, talkers
│ │ Running migrations:
│ │ No migrations to apply.
│ └ job/setup-and-migrate-db-rev14 po/setup-and-migrate-db-rev14-k5hhf container/setup-and-migrate-db logs
│
│ ┌ Status progress
│ │ DEPLOYMENT REPLICAS AVAILABLE UP-TO-DATE
│ │ werf-guide-app 1/1 1 1
│ │ STATEFULSET REPLICAS READY UP-TO-DATE
│ │ minio 1/1 1 1
│ │ mysql 1/1 1 1
│ │ JOB ACTIVE DURATION SUCCEEDED/FAILED
│ │ setup-and-migrate-db-rev14 0 3s 1/0
│ │ │ POD READY RESTARTS STATUS
│ │ └── and-migrate-db-rev14-k5hhf 0/1 0 Completed
│ └ Status progress
└ Waiting for resources to become ready (2.08 seconds)
┌ Waiting for resources elimination: jobs/setup-and-migrate-db-rev13
└ Waiting for resources elimination: jobs/setup-and-migrate-db-rev13 (0.21 seconds)
Release "werf-guide-app" has been upgraded. Happy Helming!
NAME: werf-guide-app
LAST DEPLOYED: Wed Aug 24 20:47:55 2022
LAST PHASE: rollout
LAST STAGE: 0
NAMESPACE: werf-guide-app
STATUS: deployed
REVISION: 14
TEST SUITE: None
Running time 14.16 seconds
Now let’s access the /download endpoint to get the file from S3:
curl http://werf-guide-app.test/download
Since we haven’t uploaded any files yet, we’ll get this:
You haven't uploaded anything yet.
Now let’s create a new file and upload it to the S3 storage:
echo "This is file content." > file.txt
curl -F "file=@file.txt" http://werf-guide-app.test/upload
"This is file content." | Out-File -Encoding ascii -FilePath file.txt
curl.exe -F "file=@file.txt" http://werf-guide-app.test/upload
The expected output indicates that the file has been successfully added to the storage:
File uploaded.
Let’s try to pull the file from the storage again:
curl http://werf-guide-app.test/download
You should see the file content:
This is file content.
Let’s make sure that the file gets saved directly to the storage and pulled from it. To do this, run the container having the mc tool to interact with MinIO:
kubectl run mc --image=minio/mc:RELEASE.2023-10-04T06-52-56Z --rm -it --command -- bash
Now, execute the following commands in the container’s shell:
# Connect to MinIO
mc alias set minio http://minio:9000 minioadmin minioadmin
# Get the content of file stored in S3
mc cat "minio/werf-guide-app/$(mc ls minio/werf-guide-app | awk 'NR==1 {print $5}')"
The expected outcome:
This is file content.
In this chapter, we learned how to store files in the S3-compatible object storage instead of the container file system. With this approach, the application Pods can be created and deleted without issues: files are stored safely, and any application replica can quickly access them. At the same time, the file system on Kubernetes nodes will not be filled with unnecessary files.
Keep in mind that you can only store data you can afford to lose in a container. All other data must be stored in the appropriate database/storage. This approach is endorsed by many, e.g. you can find it in the best practices by Google Cloud engineers.
