With MKE, you can add labels to your nodes. Labels are metadata that describe the node, like its role (development, QA, production), its region (US, EU, APAC), or the kind of disk (HDD, SSD). Once you have labeled your nodes, you can add deployment constraints to your services, to ensure they are scheduled on a node with a specific label.
For example, you can apply labels based on their role in the development lifecycle, or the hardware resources they have.
Don’t create labels for authorization and permissions to resources. Instead, use resource sets, either MKE collections or Kubernetes namespaces, to organize access to your cluster.
In this example, we’ll apply the ssd
label to a node. Next, we’ll
deploy a service with a deployment constraint to make sure the service
is always scheduled to run on a node that has the ssd
label.
disk
and a value of ssd
.You can also do this from the CLI by running:
docker node update --label-add <key>=<value> <node-id>
When deploying a service, you can specify constraints, so that the service gets scheduled only on a node that has a label that fulfills all of the constraints you specify.
In this example, when users deploy a service, they can add a constraint
for the service to be scheduled only on nodes that have SSD storage:
node.labels.disk == ssd
.
Navigate to the Stacks page.
Name the new stack “wordpress”.
Under Orchestrator Mode, select Swarm Services.
In the docker-compose.yml editor, paste the following stack file.
version: "3.1"
services:
db:
image: mysql:5.7
deploy:
placement:
constraints:
- node.labels.disk == ssd
restart_policy:
condition: on-failure
networks:
- wordpress-net
environment:
MYSQL_ROOT_PASSWORD: wordpress
MYSQL_DATABASE: wordpress
MYSQL_USER: wordpress
MYSQL_PASSWORD: wordpress
wordpress:
depends_on:
- db
image: wordpress:latest
deploy:
replicas: 1
placement:
constraints:
- node.labels.disk == ssd
restart_policy:
condition: on-failure
max_attempts: 3
networks:
- wordpress-net
ports:
- "8000:80"
environment:
WORDPRESS_DB_HOST: db:3306
WORDPRESS_DB_PASSWORD: wordpress
networks:
wordpress-net:
Click Create to deploy the stack, and when the stack deploys, click Done.
Navigate to the Nodes page, and click the node that has the
disk
label. In the details pane, click the Inspect Resource
drop-down menu and select Containers.
Dismiss the filter and navigate to the Nodes page.
Click a node that doesn’t have the disk
label. In the details pane,
click the Inspect Resource drop-down menu and select Containers.
There are no WordPress containers scheduled on the node. Dismiss the
filter.
You can declare the deployment constraints in your docker-compose.yml file or when you’re creating a stack. Also, you can apply them when you’re creating a service.
To check if a service has deployment constraints, navigate to the Services page and choose the service that you want to check. In the details pane, click Constraints to list the constraint labels.
To edit the constraints on the service, click Configure and select Details to open the Update Service page. Click Scheduling to view the constraints.
You can add or remove deployment constraints on this page.