Multinode Deployments

This guide explains how to deploy Dynamo workloads across multiple nodes. Multinode deployments enable you to scale compute-intensive LLM workloads across multiple physical machines, maximizing GPU utilization and supporting larger models.

Overview

Dynamo supports multinode deployments through the multinode section in resource specifications. This allows you to:

• Distribute workloads across multiple physical nodes
• Scale GPU resources beyond a single machine
• Support large models requiring extensive tensor parallelism
• Achieve high availability and fault tolerance

Basic requirements

• Kubernetes Cluster: Version 1.24 or later
• GPU Nodes: Multiple nodes with NVIDIA GPUs
• High-Speed Networking: InfiniBand, RoCE, or high-bandwidth Ethernet (recommended for optimal performance)

Advanced Multinode Orchestration

Using Grove (default)

For sophisticated multinode deployments, Dynamo integrates with advanced Kubernetes orchestration systems:

• Grove: Network topology-aware gang scheduling and auto-scaling for AI workloads
• KAI-Scheduler: Kubernetes native scheduler optimized for AI workloads at scale

These systems provide enhanced scheduling capabilities including topology-aware placement, gang scheduling, and coordinated auto-scaling across multiple nodes.

Features Enabled with Grove:

• Declarative composition of AI workloads
• Multi-level horizontal auto-scaling
• Custom startup ordering for components
• Resource-aware rolling updates

KAI-Scheduler is a Kubernetes native scheduler optimized for AI workloads at large scale.

Features Enabled with KAI-Scheduler:

• Gang scheduling
• Network topology-aware pod placement
• AI workload-optimized scheduling algorithms
• GPU resource awareness and allocation
• Support for complex scheduling constraints
• Integration with Grove for enhanced capabilities
• Performance optimizations for large-scale deployments

Prerequisites

• Grove installed on the cluster
• (Optional) KAI-Scheduler installed on the cluster with the default queue name dynamo created. If no queue annotation is specified on the DGD resource, the operator uses the dynamo queue by default. Custom queue names can be specified via the nvidia.com/kai-scheduler-queue annotation, but the queue must exist in the cluster before deployment.

KAI-Scheduler is optional but recommended for advanced scheduling capabilities.

Using LWS and Volcano

LWS is a simple multinode deployment mechanism that allows you to deploy a workload across multiple nodes.

• LWS: LWS Installation
• Volcano: Volcano Installation

Volcano is a Kubernetes native scheduler optimized for AI workloads at scale. It is used in conjunction with LWS to provide gang scheduling support.

Core Concepts

Orchestrator Selection Algorithm

Dynamo automatically selects the best available orchestrator for multinode deployments using the following logic:

When Both Grove and LWS are Available:

• Grove is selected by default (recommended for advanced AI workloads)
• LWS is selected if you explicitly set nvidia.com/enable-grove: "false" annotation on your DGD resource

When Only One Orchestrator is Available:

• The installed orchestrator (Grove or LWS) is automatically selected

Scheduler Integration:

• With Grove: Automatically integrates with KAI-Scheduler when available, providing:
  • Advanced queue management via nvidia.com/kai-scheduler-queue annotation
  • AI-optimized scheduling policies
  • Resource-aware workload placement
• With LWS: Uses Volcano scheduler for gang scheduling and resource coordination

Configuration Examples:

Default (Grove with KAI-Scheduler):

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apiVersion: nvidia.com/v1alpha1
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kind: DynamoGraphDeployment
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metadata:
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  name: my-multinode-deployment
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  annotations:
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    nvidia.com/kai-scheduler-queue: "dynamo"
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spec:
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  # ... your deployment spec

Note: The nvidia.com/kai-scheduler-queue annotation defaults to "dynamo". If you specify a custom queue name, ensure the queue exists in your cluster before deploying. You can verify available queues with kubectl get queues.

Force LWS usage:

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apiVersion: nvidia.com/v1alpha1
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kind: DynamoGraphDeployment
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metadata:
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  name: my-multinode-deployment
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  annotations:
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    nvidia.com/enable-grove: "false"
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spec:
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  # ... your deployment spec

The multinode Section

The multinode section in a resource specification defines how many physical nodes the workload should span:

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apiVersion: nvidia.com/v1alpha1
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kind: DynamoGraphDeployment
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metadata:
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  name: my-multinode-deployment
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spec:
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  # ... your deployment spec
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  services:
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    my-service:
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      ...
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      multinode:
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        nodeCount: 2
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      resources:
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        limits:
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          gpu: "2"            # 2 GPUs per node

GPU Distribution

The relationship between multinode.nodeCount and gpu is multiplicative:

• multinode.nodeCount: Number of physical nodes
• gpu: Number of GPUs per node
• Total GPUs: multinode.nodeCount × gpu

Example:

• multinode.nodeCount: "2" + gpu: "4" = 8 total GPUs (4 GPUs per node across 2 nodes)
• multinode.nodeCount: "4" + gpu: "8" = 32 total GPUs (8 GPUs per node across 4 nodes)

Tensor Parallelism Alignment

The tensor parallelism (tp-size or --tp) in your command/args must match the total number of GPUs:

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# Example: 2 multinode.nodeCount × 4 GPUs = 8 total GPUs
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apiVersion: nvidia.com/v1alpha1
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kind: DynamoGraphDeployment
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metadata:
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  name: my-multinode-deployment
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spec:
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  # ... your deployment spec
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  services:
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    my-service:
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      ...
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      multinode:
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        nodeCount: 2
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      resources:
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        limits:
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          gpu: "4"
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      extraPodSpec:
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        mainContainer:
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          ...
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          args:
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            # Command args must use tp-size=8
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            - "--tp-size"
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            - "8"  # Must equal multinode.nodeCount × gpu

Backend-Specific Operator Behavior

When you deploy a multinode workload, the Dynamo operator automatically applies backend-specific configurations to enable distributed execution. Understanding these automatic modifications helps troubleshoot issues and optimize your deployments.

vLLM Backend

For vLLM multinode deployments, the operator automatically selects and configures the appropriate distributed execution mode based on your parallelism settings:

Deployment Modes

The operator automatically determines the deployment mode based on your parallelism configuration:

1. Tensor/Pipeline Parallelism Mode (Single model across nodes)

• When used: When world_size > GPUs_per_node where world_size = tensor_parallel_size × pipeline_parallel_size
• Use case: Distributing a single model instance across multiple nodes using tensor or pipeline parallelism

The operator uses Ray for multi-node tensor/pipeline parallel deployments. Ray provides automatic placement group management and worker spawning across nodes.

Leader Node:

• Command: ray start --head --port=6379 && <original-vllm-command> --distributed-executor-backend ray
• Behavior: Starts Ray head node, then runs vLLM which creates a placement group spanning all Ray workers
• Probes: All health probes remain active (liveness, readiness, startup)

Worker Nodes:

• Command: ray start --address=<leader-hostname>:6379 --block
• Behavior: Joins Ray cluster and blocks; vLLM on leader spawns Ray actors to these workers
• Probes: All probes (liveness, readiness, startup) are automatically removed

2. Data Parallel Mode (Multiple model instances across nodes)

• When used: When world_size × data_parallel_size > GPUs_per_node
• Use case: Running multiple independent model instances across nodes with data parallelism (e.g., MoE models with expert parallelism)

All Nodes (Leader and Workers):

• Injected Flags:
  • --data-parallel-address <leader-hostname> - Address of the coordination server
  • --data-parallel-size-local <value> - Number of data parallel workers per node
  • --data-parallel-rpc-port 13445 - RPC port for data parallel coordination
  • --data-parallel-start-rank <value> - Starting rank for this node (calculated automatically)
• Probes: Worker probes are removed; leader probes remain active

Note: The operator intelligently injects these flags into your command regardless of command structure (direct Python commands or shell wrappers)

Why Ray for Multi-Node TP/PP?

vLLM supports two distributed executor backends: ray and mp. For multi-node deployments:

• Ray executor: vLLM creates a placement group and spawns Ray actors across the cluster. Workers don’t run vLLM directly - the leader’s vLLM process manages everything.
• mp executor: Each node must run its own vLLM process with --nnodes, --node-rank, --master-addr, --master-port. This approach is more complex to orchestrate.

The Dynamo operator uses Ray because:

1. It aligns with vLLM’s official multi-node documentation (see multi-node-serving.sh)
2. Simpler orchestration - only the leader runs vLLM, workers just need Ray agents
3. vLLM automatically handles placement group creation and worker management

Compilation Cache Support

When a volume mount is configured with useAsCompilationCache: true, the operator automatically sets:

• VLLM_CACHE_ROOT: Environment variable pointing to the cache mount point

SGLang Backend

For SGLang multinode deployments, the operator injects distributed training parameters:

Leader Node

• Distributed Flags: Injects --dist-init-addr <leader-hostname>:29500 --nnodes <count> --node-rank 0
• Probes: All health probes remain active

Worker Nodes

• Distributed Flags: Injects --dist-init-addr <leader-hostname>:29500 --nnodes <count> --node-rank <dynamic-rank>
  • The node-rank is automatically determined from the pod’s stateful identity
• Probes: All probes (liveness, readiness, startup) are automatically removed

Note: The operator intelligently injects these flags regardless of your command structure (direct Python commands or shell wrappers).

TensorRT-LLM Backend

For TensorRT-LLM multinode deployments, the operator configures MPI-based communication:

Leader Node

• SSH Configuration: Automatically sets up SSH keys and configuration from a Kubernetes secret
• MPI Command: Wraps your command in an mpirun command with:
  • Proper host list including all worker nodes
  • SSH configuration for passwordless authentication on port 2222
  • Environment variable propagation to all nodes
  • Activation of the Dynamo virtual environment
• Probes: All health probes remain active

Worker Nodes

• SSH Daemon: Replaces your command with SSH daemon setup and execution
  • Generates host keys in user-writable directories (non-privileged)
  • Configures SSH daemon to listen on port 2222
  • Sets up authorized keys for leader access
• Probes:
  • Liveness and Startup: Removed (workers run SSH daemon, not the main application)
  • Readiness: Replaced with TCP socket check on SSH port 2222
    • Initial Delay: 20 seconds
    • Period: 20 seconds
    • Timeout: 5 seconds
    • Failure Threshold: 10

Additional Configuration

• Environment Variable: OMPI_MCA_orte_keep_fqdn_hostnames=1 is added to all nodes
• SSH Volume: Automatically mounts the SSH keypair secret (typically named mpirun-ssh-key-<deployment-name>)
• Automatic SSH key generation: The operator automatically generates the SSH keypair secret when it detects a multi-node DynamoGraphDeployment. No manual secret creation is required.

Compilation Cache Configuration

The operator supports compilation cache volumes for backend-specific optimization:

To enable compilation cache, add a volume mount with useAsCompilationCache: true in your component specification. For vLLM, the operator will automatically configure the necessary environment variables. For other backends, volume mounts are created, but additional environment configuration may be required until upstream support is added.

Next Steps

For additional support and examples, see the working multinode configurations in:

• SGLang: examples/backends/sglang/deploy/
• TensorRT-LLM: examples/backends/trtllm/deploy/
• vLLM: examples/backends/vllm/deploy/

These examples demonstrate proper usage of the multinode section with corresponding gpu limits and correct tp-size configuration.