How would a migration from infrastructure work (e.g. from PostGre to CORDA or Hyperledger Fabric) - in Canton context?

Questions
1

Hi
I assume the participant nodes wont change in such situations, how does one go about migrating a domain from one underlying ledger to another?

thanks

2

Hi Vivek,
There’s no direct support for migrating the domain data from one infrastructure to another. However, as all relevant Daml data rests at the participants anyway, you can simply transfer the Daml contracts from the old Canton domain to the new one, using Canton’s preview feature for multi-domain support. In detail:

  1. Stop all applications using the participants and wait until there is no more activity on the old domain Dold.
  2. Spin up the new infrastructure as a new domain Dnew.
  3. Connect all participants to Dnew.
  4. Move each contract ID using the preview feature participantX.transfer.execute(stakeholder, contract-id, Dold, Dnew)
  5. Disconnect the participants from the old domain Dold.
  6. Resume the applications.

Then you can dismantle the old domain Dold if you wish.

Step 4 must be currently run for each active contract once. So this probably does not scale to huge sets of active contracts. But this is merely an engineering issue; the fundamental idea can be made to scale (provided there is enough demand to warrant the engineering effort).

1 Like
3

Hello Vivek and thank you for your question.

In addition to the answer by Andreas there is another way to look at the scenario in question:

Your intuition that the participant nodes don’t have to change is good although I see two ways to approach this based on two slightly different scenarios documented in the Operational Processes section of the canton manual:

  1. Recovering from a lost domain describes a scenario in which a domain is replaced and the associated active contracts are transferred to a different domain. In the scenario that you describe the “from”-domain corresponds to the “lost” domain. In that approach the participants indeed do not change per-se.
  2. Alternatively the Section on Importing existing contracts takes the approach of building a new canton ledger, but that is likely overkill as you would potentially have to move a large number of contracts.

Best regards,
– Oliver

1 Like
4

Hi, I have a related “Canton newbye” follow-up question: contracts migration is needed because a contract pertains to a domain.

According to my understanding of the white paper, though, a contract does not really “reside” in a domain (which is essentially messaging infrastructure) but is rather associated to one: what is this association used for?

5

Hi @fabio.tudone

If you want to dive into composability, please have a look at the corresponding tutorial: Composability — Canton 1.0.0-SNAPSHOT [0J documentation

You are right that the contract does not reside on the domain. Rather, the domain is the currently agreed synchronisation point of the stakeholders. Effectively, when deciding about a valid state, we need to establish an order of attempted changes, and that’s done by having the domain order the encrypted messages such that every participant receives the transactions in the same order.

The agreement that a certain domain is responsible for the ordering is a temporary one and can be changed by a transfer.

Cheers,
Ratko

1 Like
6

Thanks @Ratko_Veprek! I’ll go through the tutorial (and possibly come back with more questions).