Node Selection

Node selection determines which server in the zone will host a space. Knot can automatically select the best server based on availability and runtime requirements, or you can manually specify a server during space creation. For local-container spaces, that assignment can still be changed while the space remains stopped when the template allows node migration.

Overview

When multiple servers are available in a zone, you can choose where a space is deployed:

• Automatic Selection (default): Knot selects the best available server
• Manual Selection: You choose a specific server when creating the space

If a local-container space has not been started yet, you can still edit it and change the assigned server before the first start. After a space has been started, reassignment is only available for stopped spaces whose template explicitly allows node migration.

If only one server in the zone can run the space, that server is automatically selected.

Automatic Selection

When creating a space, leave the server selection set to Auto to let Knot choose the best server.

Selection Criteria

Knot evaluates servers in the zone and selects based on the following priorities:

1. Runtime Requirements

   • If the template specifies a container runtime, only servers with that runtime are considered
   • If no runtime is specified, Knot uses the configured preference order: Docker > Podman > Apple Containers

2. Zone Affinity

   • Only servers in the same zone as the request are considered for local containers (Docker, Podman, Apple Containers)
   • Nomad deployments are handled separately by the Nomad scheduler

3. Load Balancing

   • The server with the lowest number of allocated spaces is selected
   • If servers have equal load, one is chosen at random

Runtime Detection and Configuration

Each server in the zone exposes which container runtimes it supports:

• Docker: Detected via docker info
• Podman: Detected via podman info
• Apple Containers: Detected via container system status

The runtime preference order is defined in your knot.toml configuration:

[server.docker]
  host = "unix:///var/run/docker.sock"

[server.podman]
  host = "unix:///var/run/podman.sock"

Knot automatically detects available runtimes. The preference order is:

1. Docker
2. Podman
3. Apple Containers (macOS only)

Only servers capable of running the space’s required runtime are shown as options when creating a space.

Manual Selection

To manually select a server for your space:

1. Navigate to the space creation dialog
2. In the server selection dropdown, choose a specific server instead of Auto
3. Complete the space creation as normal

When to Use Manual Selection

• You need to place a space on a server with specific resources
• You’re testing deployment on a particular server
• You have affinity requirements (e.g., database and application on the same server)
• A server has specialized hardware or configurations

Node Affinity

Spaces can be configured with node affinity for persistent placement:

• Automatic (default): No specific server preference; Knot chooses based on current load
• Manual: Space is assigned to a specific server and will prefer that server on restart

For stopped local-container spaces, you can edit the space and switch the assigned server before starting it. Before first start this is always available; after that it depends on the template’s node migration setting. This is the manual migration path in OSS. Automatic failed-node recovery, detecting a failed node and migrating spaces to a live node, requires Knot Pro Pro .

Node affinity is stored with the space configuration and persists across space restarts.

Cluster Considerations

In a multi-server cluster:

• Server load information is updated in real-time
• Automatic selection ensures even distribution across available servers

For high availability, consider:

• Distributing spaces across multiple servers
• Using manual selection for critical services
• Monitoring server resource utilization

Troubleshooting

No Servers Available

If no servers appear in the selection dropdown:

• Verify servers are online and in the same zone
• Check that the required container runtime is available on at least one server
• Ensure your user has permissions to create spaces on the servers

Server Not Listed

If an expected server doesn’t appear:

• Confirm the server is in the same zone
• Verify the container runtime matches the template requirements
• Check the server’s connectivity and agent status

Wrong Server Selected

If automatic selection chooses an unexpected server:

• Review the runtime preference order in knot.toml
• Check current space allocation across servers
• Use manual selection to override automatic behavior