# Understanding Kubernetes: Part 24 Taints and Tolerations

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📢 If you’ve been following our Kubernetes series 2025, welcome back! For new readers, check out [**Part 23 Node Selector**](https://medium.com/@techwithpatil/understanding-kubernetes-part-23-node-selector-faf9e415ea02)

#### What is a Taint?

A **taint** is a property applied to a node that prevents Pods from being scheduled on it unless they have a matching **toleration**.

#### What is a Toleration?

A **toleration** is a property set in a Pod specification that allows the Pod to be scheduled on a tainted node.

***

#### Use Cases

Taints and Tolerations are useful in various scenarios:

#### 1. Dedicated Nodes for Specific Workloads

* Running GPU workloads only on specialized GPU nodes.
* Ensuring that high-priority applications run on high-performance nodes.

#### 2. Isolation of Workloads

* Keeping test workloads separate from production environments.
* Running database workloads on dedicated nodes.

#### 3. Preventing Scheduling on Faulty or Maintenance Nodes

* Marking nodes as unschedulable during planned maintenance.
* Isolating nodes that experience hardware or software failures.

***

#### Taint Syntax

A **taint** is applied to a node using the following command:

```
kubectl taint nodes <node-name> <key>=<value>:<effect>
```

Where:

* `<key>`: Identifier for the taint (e.g., `environment`)
* `<value>`: A descriptive value (e.g., `test`)
* `<effect>`: Defines how the taint behaves:
* `NoSchedule`: Prevents scheduling unless the Pod has a matching toleration.
* `PreferNoSchedule`: Avoids scheduling if possible but allows it if no other options exist.
* `NoExecute`: Evicts existing Pods that don't tolerate the taint.
* <br>

**Example: Applying a Taint**

To dedicate a node for database workloads:

```
kubectl taint nodes node-1 dedicated=db:NoSchedule
```

This ensures that only Pods with a matching toleration can be scheduled on `node-1`.

#### Tolerations in Pod Definition

To allow a Pod to run on a tainted node, we add a **toleration** in its YAML configuration.

**Example: Toleration for a Database Pod**

```
apiVersion: v1
kind: Pod
metadata:
  name: db-pod
spec:
  tolerations:
    - key: "dedicated"
      operator: "Equal"
      value: "db"
      effect: "NoSchedule"
  containers:
    - name: postgres
      image: postgres
```

This Pod can be scheduled on the node `node-1`, which was tainted with `dedicated=db:NoSchedule`.

***

#### Removing Taints and Tolerations

If you need to remove a taint from a node, run:

```
kubectl taint nodes node-1 dedicated=db:NoSchedule-
```

The `-` at the end removes the taint.

Tolerations are part of a Pod definition, and removing them from the Pod specification means it will no longer tolerate tainted nodes.

***

#### In My Previous Role

As a Senior DevOps Engineer, I used Kubernetes taints to optimize workload placement and resource utilization.

* **GPU Workloads**: Applied taints on GPU nodes to ensure that only ML/AI workloads could be scheduled on them, preventing other workloads from consuming GPU resources.
* **High-Performance Nodes**: Used taints to reserve high-memory and high-CPU nodes for critical applications, ensuring they had dedicated resources.
* **Node Maintenance**: Applied NoExecute taints to nodes undergoing updates, ensuring that existing workloads were gracefully evicted and rescheduled on healthy nodes.

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