Select least-loaded eligible node when creating containers

[Copilot]

Container creation previously selected the first node matching eligibility filters, which could concentrate workloads on one node. This change updates placement to select the eligible node with the fewest existing containers.

• Placement strategy update

  • Keep existing eligibility filters (siteId, API access credentials, optional nvidiaAvailable).
  • Replace single-node lookup with least-load selection across all eligible nodes.

• Load-aware node selection

  • Fetch eligible node IDs.
  • Aggregate container counts per eligible node.
  • Choose the node with the smallest container count.
  • Apply deterministic tie-break by lowest node ID.

• Behavior preserved

  • Existing error paths remain unchanged when no eligible node exists (including NVIDIA-specific case).

const eligibleNodes = await Node.findAll({ where: nodeWhere, attributes: ['id'] });
const eligibleNodeIds = eligibleNodes.map(({ id }) => id);

const nodeContainerCounts = eligibleNodeIds.length === 0 ? [] : await Container.findAll({
  where: { nodeId: eligibleNodeIds },
  attributes: ['nodeId', [Sequelize.fn('COUNT', Sequelize.col('id')), 'containerCount']],
  group: ['nodeId'],
  raw: true
});

const countByNodeId = new Map(
  nodeContainerCounts.map(({ nodeId, containerCount }) => [Number(nodeId), Number(containerCount)])
);

const node = eligibleNodes.reduce((leastLoadedNode, candidateNode) => {
  const candidateCount = countByNodeId.get(candidateNode.id) || 0;
  if (!leastLoadedNode) return candidateNode;
  const leastLoadedCount = countByNodeId.get(leastLoadedNode.id) || 0;
  if (candidateCount < leastLoadedCount) return candidateNode;
  if (candidateCount === leastLoadedCount && candidateNode.id < leastLoadedNode.id) return candidateNode;
  return leastLoadedNode;
}, null);