> Full Neon documentation index: https://neon.com/docs/llms.txt

# Distributed hyperparameter tuning with Optuna, Lakebase Postgres, and Kubernetes

Use Lakebase Postgres to orchestrate multi-node hyperparameter tuning for your scikit-learn, XGBoost, PyTorch, and TensorFlow/Keras models on a Kubernetes cluster

In this guide, you'll learn how to set up distributed hyperparameter tuning for machine learning models across multiple nodes using Kubernetes. You'll use Optuna, a Bayesian optimization library, to tune models built with libraries like scikit-learn, XGBoost, PyTorch, and TensorFlow/Keras.

To coordinate the trials, you'll use Lakebase Postgres on Neon as Optuna's shared storage backend. Kubernetes runs the trials in parallel Docker containers, and every worker reads and writes the same study in Postgres.

## Prerequisites

Before you begin, make sure you have the following tools and services set up:

- `Neon`: A Neon account to host your Postgres database. If you don't have an account yet, [sign up here](https://console.neon.tech/signup).
- `Minikube`: For running a local Kubernetes cluster. You can install it by following the official [Minikube installation guide](https://minikube.sigs.k8s.io/docs/start).
- `kubectl`: Kubernetes command-line tool for interacting with your cluster. Follow the [kubectl installation instructions](https://kubernetes.io/docs/tasks/tools/) to get started.
- `Docker`: For containerizing your applications. If you don't have it installed, check out the [Docker installation guide](https://docs.docker.com/engine/install/).
- `Python`: To create, train, and optimize machine learning models. You can download Python from the [official website](https://www.python.org/downloads/).

## Overview

Hyperparameters have a large effect on machine learning model performance. Unlike parameters learned during training, hyperparameters (like learning rates, batch sizes, or the number of layers in a neural network) need to be set in advance. Tuning them can improve accuracy or reduce training time.

Bayesian optimization is an efficient method for hyperparameter tuning. Unlike traditional approaches like grid or random search, Bayesian optimization builds a probabilistic model of the objective function to help it sample which hyperparameters to test next, which reduces the number of experiments needed, saving time and compute.

Distributing hyperparameter tuning across multiple nodes allows each trial to run independently on its own machine, enabling multiple configurations to be tested simultaneously and speeding up the search process. The nodes need a shared place to coordinate, and Lakebase Postgres works well for this. Compute autoscales with the workload and scales to zero when idle, so you don't pay for compute between tuning runs (storage is still billed). The database maintains the state of the hyperparameter tuning process, storing the results of each trial and coordinating the distribution of new trials to available nodes.

Kubernetes, a container orchestration platform, runs the same task concurrently across multiple nodes, so each node handles a separate trial. It also manages resources per node and restarts failed workloads, which makes the training process fault tolerant.

In this guide, you'll combine Optuna, Kubernetes, and Lakebase Postgres to build a system for distributed tuning of your PyTorch, TensorFlow/Keras, scikit-learn, and XGBoost models.

## Hyperparameter tuning

Optuna organizes hyperparameter tuning into studies, which are collections of trials. A study represents a single optimization run, and each trial within the study corresponds to a set of hyperparameters to be evaluated. Optuna uses a study to manage the optimization process, keeping track of the trials, their results, and the best hyperparameters found so far.

When you create a study, you can specify various parameters like the study name, the direction of optimization (minimize or maximize), and the storage backend. The storage backend is where Optuna stores the study data, including the trials and their results. By using a persistent storage backend like Lakebase Postgres, you can save the state of the optimization process, allowing all nodes to access the same study and coordinate the tuning process.

A study is created like so:

```python {4,5}
if __name__ == "__main__":
    study = optuna.create_study(
        study_name="sklearn_example",
        storage=os.environ["DATABASE_URL"],
        load_if_exists=True,
        direction="maximize",
    )
    study.optimize(objective, n_trials=100)
```

In the case of the distributed training, the `load_if_exists` parameter is set to `True` to load an existing study if it already exists, allowing nodes to join the optimization process.

Based on your machine learning library of choice, you can define an `objective` function that takes a `trial` object as input and returns a metric to optimize. The sections below show how to define the `objective` function for scikit-learn, XGBoost, PyTorch, and TensorFlow/Keras models using test datasets.

To follow along, name your Python script `hyperparam_optimization.py`.

### sklearn

scikit-learn has a wide range of models, but in this example you'll compare a Support Vector Classifier and a Random Forest Classifier, and their hyperparameter configurations. For the SVC, you will optimize the strength of the regularization parameter `C`, while for the RF, you will optimize the maximum depth of the trees `max_depth`.

```python
import os
import optuna
import sklearn.datasets
import sklearn.ensemble
import sklearn.model_selection
import sklearn.svm

def objective(trial):
    iris = sklearn.datasets.load_iris()
    x, y = iris.data, iris.target

    classifier_name = trial.suggest_categorical("classifier", ["SVC", "RandomForest"])
    if classifier_name == "SVC":
        svc_c = trial.suggest_float("svc_c", 1e-10, 1e10, log=True)
        classifier_obj = sklearn.svm.SVC(C=svc_c, gamma="auto")
    else:
        rf_max_depth = trial.suggest_int("rf_max_depth", 2, 32, log=True)
        classifier_obj = sklearn.ensemble.RandomForestClassifier(
            max_depth=rf_max_depth, n_estimators=10
        )

    score = sklearn.model_selection.cross_val_score(classifier_obj, x, y, n_jobs=-1, cv=3)
    accuracy = score.mean()
    return accuracy


if __name__ == "__main__":
    study = optuna.create_study(
        study_name="sklearn_example",
        storage=os.environ["DATABASE_URL"],
        load_if_exists=True,
        direction="maximize",
    )
    study.optimize(objective, n_trials=100)
    print(study.best_trial)
```

### xgboost

Gradient boosting is a common choice for tabular data, and XGBoost is a widely used library for it. These models are sensitive to hyperparameter choice. In this example, you will optimize the booster type, regularization weights, sampling ratios, and tree complexity parameters.

```python
import numpy as np
import os
import optuna
import sklearn.datasets
import sklearn.metrics
from sklearn.model_selection import train_test_split
import xgboost as xgb


def objective(trial):
    (data, target) = sklearn.datasets.load_breast_cancer(return_X_y=True)
    train_x, valid_x, train_y, valid_y = train_test_split(data, target, test_size=0.25)
    dtrain = xgb.DMatrix(train_x, label=train_y)
    dvalid = xgb.DMatrix(valid_x, label=valid_y)

    param = {
        "verbosity": 0,
        "objective": "binary:logistic",
        # use exact for small dataset.
        "tree_method": "exact",
        # defines booster, gblinear for linear functions.
        "booster": trial.suggest_categorical("booster", ["gbtree", "gblinear", "dart"]),
        # L2 regularization weight.
        "lambda": trial.suggest_float("lambda", 1e-8, 1.0, log=True),
        # L1 regularization weight.
        "alpha": trial.suggest_float("alpha", 1e-8, 1.0, log=True),
        # sampling ratio for training data.
        "subsample": trial.suggest_float("subsample", 0.2, 1.0),
        # sampling according to each tree.
        "colsample_bytree": trial.suggest_float("colsample_bytree", 0.2, 1.0),
    }

    if param["booster"] in ["gbtree", "dart"]:
        # maximum depth of the tree, signifies complexity of the tree.
        param["max_depth"] = trial.suggest_int("max_depth", 3, 9, step=2)
        # minimum child weight, larger the term more conservative the tree.
        param["min_child_weight"] = trial.suggest_int("min_child_weight", 2, 10)
        param["eta"] = trial.suggest_float("eta", 1e-8, 1.0, log=True)
        # defines how selective algorithm is.
        param["gamma"] = trial.suggest_float("gamma", 1e-8, 1.0, log=True)
        param["grow_policy"] = trial.suggest_categorical("grow_policy", ["depthwise", "lossguide"])

    if param["booster"] == "dart":
        param["sample_type"] = trial.suggest_categorical("sample_type", ["uniform", "weighted"])
        param["normalize_type"] = trial.suggest_categorical("normalize_type", ["tree", "forest"])
        param["rate_drop"] = trial.suggest_float("rate_drop", 1e-8, 1.0, log=True)
        param["skip_drop"] = trial.suggest_float("skip_drop", 1e-8, 1.0, log=True)

    bst = xgb.train(param, dtrain)
    preds = bst.predict(dvalid)
    pred_labels = np.rint(preds)
    accuracy = sklearn.metrics.accuracy_score(valid_y, pred_labels)
    return accuracy

if __name__ == "__main__":
    study = optuna.create_study(
        study_name="xgboost_example",
        storage=os.environ["DATABASE_URL"],
        load_if_exists=True,
        direction="maximize",
    )
    study.optimize(objective, n_trials=100)
```

### PyTorch

PyTorch is widely used for deep learning research and many other machine learning tasks. In this example, you will optimize the number of layers, hidden units, and dropout ratios in a feedforward neural network for the FashionMNIST dataset, a popular benchmark for image classification.

```python
import os
import optuna
from optuna.trial import TrialState
import torch
import torch.nn as nn
import torch.nn.functional as F
import torch.optim as optim
import torch.utils.data
from torchvision import datasets
from torchvision import transforms


DEVICE = torch.device("cpu")
BATCHSIZE = 128
CLASSES = 10
DIR = os.getcwd()
EPOCHS = 10
N_TRAIN_EXAMPLES = BATCHSIZE * 30
N_VALID_EXAMPLES = BATCHSIZE * 10


def define_model(trial):
    n_layers = trial.suggest_int("n_layers", 1, 3)
    layers = []

    in_features = 28 * 28
    for i in range(n_layers):
        out_features = trial.suggest_int("n_units_l{}".format(i), 4, 128)
        layers.append(nn.Linear(in_features, out_features))
        layers.append(nn.ReLU())
        p = trial.suggest_float("dropout_l{}".format(i), 0.2, 0.5)
        layers.append(nn.Dropout(p))

        in_features = out_features
    layers.append(nn.Linear(in_features, CLASSES))
    layers.append(nn.LogSoftmax(dim=1))

    return nn.Sequential(*layers)


def get_mnist():
    train_loader = torch.utils.data.DataLoader(
        datasets.FashionMNIST(DIR, train=True, download=True, transform=transforms.ToTensor()),
        batch_size=BATCHSIZE,
        shuffle=True,
    )
    valid_loader = torch.utils.data.DataLoader(
        datasets.FashionMNIST(DIR, train=False, transform=transforms.ToTensor()),
        batch_size=BATCHSIZE,
        shuffle=True,
    )

    return train_loader, valid_loader


def objective(trial):
    model = define_model(trial).to(DEVICE)

    # Generate the optimizers.
    optimizer_name = trial.suggest_categorical("optimizer", ["Adam", "RMSprop", "SGD"])
    lr = trial.suggest_float("lr", 1e-5, 1e-1, log=True)
    optimizer = getattr(optim, optimizer_name)(model.parameters(), lr=lr)

    train_loader, valid_loader = get_mnist()

    for epoch in range(EPOCHS):
        model.train()
        for batch_idx, (data, target) in enumerate(train_loader):
            data, target = data.view(data.size(0), -1).to(DEVICE), target.to(DEVICE)

            optimizer.zero_grad()
            output = model(data)
            loss = F.nll_loss(output, target)
            loss.backward()
            optimizer.step()

        model.eval()
        correct = 0
        with torch.no_grad():
            for batch_idx, (data, target) in enumerate(valid_loader):
                if batch_idx * BATCHSIZE >= N_VALID_EXAMPLES:
                    break
                data, target = data.view(data.size(0), -1).to(DEVICE), target.to(DEVICE)
                output = model(data)
                pred = output.argmax(dim=1, keepdim=True)
                correct += pred.eq(target.view_as(pred)).sum().item()

        accuracy = correct / min(len(valid_loader.dataset), N_VALID_EXAMPLES)

        trial.report(accuracy, epoch)

        if trial.should_prune():
            raise optuna.exceptions.TrialPruned()

    return accuracy


if __name__ == "__main__":
    study = optuna.create_study(
        study_name="pytorch_example",
        storage=os.environ["DATABASE_URL"],
        load_if_exists=True,
        direction="maximize",
    )
    study.optimize(objective, n_trials=100, timeout=600)
```

### tf.keras

Keras with the TensorFlow backend is popular for its simple API. In this example, you will optimize the number of filters, kernel size, strides, activation functions, and learning rate in a convolutional neural network for the MNIST dataset.

```python
import urllib
import os

import optuna
from tensorflow.keras.backend import clear_session
from tensorflow.keras.datasets import mnist
from tensorflow.keras.layers import Conv2D
from tensorflow.keras.layers import Dense
from tensorflow.keras.layers import Flatten
from tensorflow.keras.models import Sequential
from tensorflow.keras.optimizers import RMSprop

N_TRAIN_EXAMPLES = 3000
N_VALID_EXAMPLES = 1000
BATCHSIZE = 128
CLASSES = 10
EPOCHS = 10


def objective(trial):
    clear_session()

    (x_train, y_train), (x_valid, y_valid) = mnist.load_data()
    img_x, img_y = x_train.shape[1], x_train.shape[2]
    x_train = x_train.reshape(-1, img_x, img_y, 1)[:N_TRAIN_EXAMPLES].astype("float32") / 255
    x_valid = x_valid.reshape(-1, img_x, img_y, 1)[:N_VALID_EXAMPLES].astype("float32") / 255
    y_train = y_train[:N_TRAIN_EXAMPLES]
    y_valid = y_valid[:N_VALID_EXAMPLES]
    input_shape = (img_x, img_y, 1)

    model = Sequential()
    model.add(
        Conv2D(
            filters=trial.suggest_categorical("filters", [32, 64]),
            kernel_size=trial.suggest_categorical("kernel_size", [3, 5]),
            strides=trial.suggest_categorical("strides", [1, 2]),
            activation=trial.suggest_categorical("activation", ["relu", "linear"]),
            input_shape=input_shape,
        )
    )
    model.add(Flatten())
    model.add(Dense(CLASSES, activation="softmax"))

    learning_rate = trial.suggest_float("learning_rate", 1e-5, 1e-1, log=True)
    model.compile(
        loss="sparse_categorical_crossentropy",
        optimizer=RMSprop(learning_rate=learning_rate),
        metrics=["accuracy"],
    )

    model.fit(
        x_train,
        y_train,
        validation_data=(x_valid, y_valid),
        shuffle=True,
        batch_size=BATCHSIZE,
        epochs=EPOCHS,
        verbose=False,
    )

    score = model.evaluate(x_valid, y_valid, verbose=0)
    return score[1]

if __name__ == "__main__":
    study = optuna.create_study(
        study_name="tfkeras_example",
        storage=os.environ["DATABASE_URL"],
        load_if_exists=True,
        direction="maximize",
    )
    study.optimize(objective, n_trials=100, timeout=600)
```

## Creating the Docker image

To run the hyperparameter tuning process in a Kubernetes cluster, you'll need to containerize your application using Docker by creating a Docker image. The Docker image will contain your Python code, dependencies, and the necessary configuration files to run.

```Dockerfile
FROM python:3.10-slim-buster

WORKDIR /usr/src/

RUN pip install --no-cache-dir optuna psycopg2-binary OTHER_DEPENDENCIES

COPY hyperparam_optimization.py .
```

Depending on the machine learning library you're using, you'll need to install the appropriate dependencies in the Docker image. Each of the examples above requires the `optuna`, and `psycopg2-binary` packages, but you'll need additional dependencies for each example:

- For scikit-learn, you'll need to install `scikit-learn`
- For XGBoost, you'll need to install `xgboost`
- For PyTorch, you'll need to install `torch` and `torchvision`
- For TensorFlow/Keras, you'll need to install `tensorflow`

You'll want to build the Docker image later, once the Kubernetes cluster is set up, so that the image is available to the Kubernetes nodes.

## Setting up Kubernetes

To run distributed hyperparameter tuning across multiple nodes, you'll need a Kubernetes cluster. For this guide, you'll use Minikube to set up a local Kubernetes cluster on your machine. Minikube is a lightweight Kubernetes distribution for local development.

To start Minikube, run the following command:

```bash
minikube start
```

This command will create a new Kubernetes cluster using the default settings. Once Minikube is up and running, you can interact with the cluster using the `kubectl` command-line tool.

To check the status of your cluster, run:

```bash
kubectl cluster-info
```

This command will display information about the Kubernetes cluster, including the API server address and the cluster services.

Now that Minikube is running, build your Docker image:

```bash
eval "$(minikube docker-env)"
docker image build -t "optuna-kubernetes:example" .
```

Note the `eval "$(minikube docker-env)"` command, which sets the Docker environment variables to point to the Minikube Docker daemon. This allows you to build the Docker image inside the Minikube cluster, making it available to the Kubernetes nodes.

To submit jobs to the Kubernetes cluster, you'll need to create a Kubernetes manifest file. This file describes the task you want to run, including the container image, command, and environment variables. You can define the number of parallel jobs to run and the restart policy for the job.

To allow the Job to access the Lakebase Postgres database, you'll need to create a Kubernetes Secret containing the database credentials. You can create the secret from a `.env` file containing the database URL like so:

```bash
kubectl create secret generic optuna-postgres-secrets --from-env-file=.env
```

where your `.env` file contains the connection string from the **Connect** modal in the Neon Console:

```bash
DATABASE_URL=YOUR_DATABASE_URL
```

Or from the raw string in the Neon Console like so:

```bash
kubectl create secret generic optuna-postgres-secrets \
    --from-literal=DATABASE_URL=YOUR_DATABASE_URL
```

Now, you can create the Kubernetes Job manifest file:

```yaml
---
apiVersion: batch/v1
kind: Job
metadata:
  name: worker
spec:
  parallelism: 3
  template:
    spec:
      restartPolicy: OnFailure
      containers:
        - name: worker
          image: optuna-kubernetes:example
          imagePullPolicy: IfNotPresent
          command:
            - python
            - hyperparam_optimization.py
          envFrom:
            - secretRef:
                name: optuna-postgres-secrets
```

Here, the manifest tells Kubernetes to launch 3 parallel jobs, each running the `hyperparam_optimization.py` script inside the Docker container, and if the job fails, Kubernetes will restart it automatically. The `envFrom` field specifies that the Job should use the `optuna-postgres-secrets` secret you just created to access the Lakebase Postgres database.

Finally, you can submit the Job to the Kubernetes cluster using the following command:

```bash
kubectl apply -f k8s-manifests.yaml
```

Now, if you run the following command, you should see the Job running in the Kubernetes cluster:

```bash
kubectl get jobs
```

and if you run the following command, you should see the 3 pods running the job:

```bash
kubectl get pods
```

## Monitoring

To monitor your Kubernetes cluster, you can use the Kubernetes Dashboard, a web-based UI for managing and monitoring your cluster. To access the Kubernetes Dashboard, run the following command:

```bash
minikube dashboard
```

Likewise, you can monitor logs of the running pods to monitor using a tool like `stern`, which allows you to tail logs from multiple pods at once:

```bash
stern .
```

The first pod creates a new study, and the other pods join it. Each pod then runs a trial, logs the result, and creates a new trial based on the previous results stored in the database.

![Stern Logs](https://neon.com/guides/images/optuna-hyperprameter-kubernetes/k8s-example-logs.png)

To see Kubernetes fault tolerance in action, you can delete one of the pods, and see that the job is automatically restarted on a new pod. First, find the running pods and choose one to delete:

```bash
kubectl get pods
```

Then, delete the pod:

```bash
kubectl delete pod <POD_NAME>
```

In the stern logs, you can see the pod getting removed, and a new pod being created to replace it, all while continuing the same study as before.

![Delete Pod Stern Logs](https://neon.com/guides/images/optuna-hyperprameter-kubernetes/deletepod-logs.png)

## Conclusion

You set up distributed hyperparameter tuning with Optuna, Lakebase Postgres, and Kubernetes, with multiple pods sharing one study. This workload has bursts of database activity followed by long idle periods, which suits Lakebase Postgres: compute autoscales during a run and scales to zero afterward.

As a next step, you can use managed Kubernetes services like Azure Kubernetes Service (AKS) or Amazon Elastic Kubernetes Service (EKS). These services can scale to hundreds of nodes. You can also store training data and model checkpoints in object storage such as Amazon S3, Azure Blob Storage, or [Neon Object Storage](https://neon.com/docs/storage/overview).

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