Cell Cloning

What Is Cell Cloning?

Cell cloning creates new network instances from the same DNA code by varying the DNA hash modifier (network seed or properties). Each clone is a separate DHT network — agents in clone A cannot directly see data in clone B even though they run identical code.

This is distinct from having multiple roles in a happ — cloning is for partitioning data within a single role.

When to Use Cloning

happ.yaml Setup

roles:
  - name: group_spaces
    provisioning:
      strategy: create
      deferred: true       # not created on install — app creates cells on demand
    dna:
      bundled: "./group_spaces.dna"
      modifiers:
        network_seed: ~
      clone_limit: 50      # allow up to 50 clones of this role

clone_limit must be set to enable cloning. If clone_limit: 0 (default), cloning is not permitted.

TypeScript Client — Creating a Clone

import { AppClient } from '@holochain/client';

// Create a new clone cell with a unique network seed:
const cloneCell = await appClient.createCloneCell({
  role_name: 'group_spaces',
  modifiers: {
    network_seed: `group-${groupId}`,  // unique seed = unique network
    properties: encode({ group_name: groupName }),
  },
  name: `Group: ${groupName}`,
});

const clonedCellId = cloneCell.cell_id;

Addressing Clone Cells

Clone cells use a composite role name format: "{role_name}.{clone_index}"

// First clone:   "group_spaces.0"
// Second clone:  "group_spaces.1"
// etc.

// Call a function on a specific clone:
const result = await appClient.callZome({
  cell_id: clonedCellId,   // or use role_name: "group_spaces.0"
  zome_name: 'group_spaces',
  fn_name: 'create_post',
  payload: { content: 'Hello group!' },
});

Enabling / Disabling Clones

// Disable a clone (data preserved, cell not running):
await appClient.disableCloneCell({ clone_cell_id: clonedCellId });

// Re-enable a previously disabled clone:
await appClient.enableCloneCell({ clone_cell_id: clonedCellId });

Key Constraints

• The maximum number of clones is set by clone_limit in happ.yaml — plan capacity upfront
• Each clone’s network seed must be unique — using the same seed creates the same network
• Cloned cells share the same WASM binary but have separate source chains and DHTs
• deferred: true is required for clonable roles — they are not provisioned on install

Reference: developer.holochain.org/build/cell-cloning/