Load Balancing for Scalable AI Model Serving

Question

Pulumi · Accepted Answer

When serving AI models, scalability is a critical factor to meet varying load demands efficiently. Load balancing helps distribute incoming network traffic across a group of backend services or servers to ensure no single server bears too much demand. By spreading the load evenly, load balancing improves responsiveness and increases the availability of applications.

In the context of cloud services, a load balancer can be a software-based network function or a managed service that operates at different layers of the OSI model – typically at layer 4 (transport) or layer 7 (application). Layer 7 load balancers can inspect the content of the traffic to make more complex routing decisions based on HTTP headers, cookies, or data within the application message.

For AI model serving, you might often want to use containerized solutions to package the model and its dependencies. Kubernetes, a container orchestrator, becomes useful here, as it supports auto-scaling and self-healing of containerized applications. Kubernetes can be combined with a load balancer to distribute traffic to the services.

Here is a conceptual program in Pulumi using Python that creates a load-balanced, scalable AI model serving setup. The program uses a Google Cloud Platform's (GCP) managed Kubernetes Engine (GKE) cluster and deploys a simple containerized application. The application is exposed via a GCP Load Balancer. This example focuses on the infrastructure setup, and you'll need to replace the sample application with your AI model serving application container.

```python
import pulumi
from pulumi_gcp.container import Cluster, NodeConfig, NodePool, ClusterNodePoolArgs
from pulumi_gcp.compute import BackendService, BackendBucket, URLMap, TargetHttpProxy, ForwardingRule
from pulumi_kubernetes import Provider
from pulumi_kubernetes.apps.v1 import Deployment
from pulumi_kubernetes.core.v1 import Service

# Create a GKE cluster
node_config = NodeConfig(
    machine_type="n1-standard-1",
    oauth_scopes=[
        "https://www.googleapis.com/auth/compute",
        "https://www.googleapis.com/auth/devstorage.read_only",
        "https://www.googleapis.com/auth/logging.write",
        "https://www.googleapis.com/auth/monitoring"
    ],
)

node_pool = NodePool("node-pool", initial_node_count=3, node_config=node_config)

cluster = Cluster("cluster",
    initial_node_count=3,
    node_config=node_config,
    node_pool=ClusterNodePoolArgs(
        name="default-pool",
        initial_node_count=3,
    ),
)

# Create a Kubernetes provider instance using the created cluster
k8s_provider = Provider("gke-k8s", kubeconfig=cluster.endpoint.apply(lambda ep: cluster.master_auth.apply(lambda auth: f"""
apiVersion: v1
clusters:
- cluster:
    certificate-authority-data: {auth.cluster_ca_certificate}
    server: https://{ep}
  name: gke-cluster
contexts:
- context:
    cluster: gke-cluster
    user: admin
  name: gke-cluster
current-context: gke-cluster
kind: Config
preferences: {{}}
users:
- name: admin
  user:
    auth-provider:
      config:
        cmd-args: config config-helper --format=json
        cmd-path: gcloud
        expiry-key: '{{.credential.token_expiry}}'
        token-key: '{{.credential.access_token}}'
      name: gcp
""")))

# Define the AI model serving application deployment
app_labels = {"app": "ai-model-server"}
app_deployment = Deployment(
    "app-deployment",
    metadata={"labels": app_labels},
    spec={
        "selector": {"matchLabels": app_labels},
        "replicas": 3,
        "template": {
            "metadata": {"labels": app_labels},
            "spec": {
                "containers": [{
                    "name": "model-server",
                    "image": "us-docker.pkg.dev/google-samples/containers/gke/hello-app:1.0"
                }]
            }
        }
    },
    opts=pulumi.ResourceOptions(provider=k8s_provider)
)

# Define the Kubernetes service to expose the AI model server deployment
app_service = Service(
    "app-service",
    metadata={"labels": app_labels},
    spec={
        "selector": app_labels,
        "type": "ClusterIP",
        "ports": [{"port": 80}]
    },
    opts=pulumi.ResourceOptions(provider=k8s_provider)
)

# Setup Load Balancer resources
backend_service = BackendService("backend-service",
    backends=[{"group": app_service.metadata.name.apply(lambda name: f"{cluster.instance_group_urls[0]}")}])

backend_bucket = BackendBucket("backend-bucket", bucket_name="my-bucket")

url_map = URLMap("url-map",
    default_service=backend_service.self_link,
    path_matchers=[{
        "name": "allpaths",
        "defaultService": backend_bucket.self_link
    }]
)

target_http_proxy = TargetHttpProxy("http-proxy",
    url_map=url_map.self_link
)

forwarding_rule = ForwardingRule("forwarding-rule",
    target=target_http_proxy.self_link,
    port_range="80"
)

# Export the IP address of the Load Balancer
pulumi.export("forwarding_rule_ip", forwarding_rule.ip_address)
```

In this program:
- **GKE Cluster**: A managed Kubernetes cluster on GCP. Using `NodeConfig` and `NodePool` to specify the type and amount of compute resources for your cluster.
- **Kubernetes Provider**: Interacts with your GKE cluster to manage Kubernetes resources.
- **AI Model Serving Deployment**: A Kubernetes `Deployment` that manages the lifecycle of your AI model serving containers.
- **Service**: A Kubernetes `Service` that provides an internal cluster IP for your model serving deployment. It can be used for intra-cluster traffic.
- **Backend Services and Load Balancer**: A GCP load balancer configuration that includes a `BackendService`, `BackendBucket`, `URLMap`, `TargetHttpProxy`, and `ForwardingRule` to manage external traffic to your AI model serving deployment.

Remember to replace `"us-docker.pkg.dev/google-samples/containers/gke/hello-app:1.0"` with the actual Docker image of your AI Model Serving application. Also, this is a basic example, and more complete solutions would need to consider aspects like HTTPS setup with SSL certificates, authorization, request logging, and more depending on the requirements.