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In the hyperledger fabric documentation, there are 2 terms used
1. Install the chaincode on peers and
2. Instantiate the chaincode on the channel

What are the major differences between these two?

In the documentation it said that a chaincode can be installed on multiple peers but can be instantiated once. I understood this point as a channel only needs the information about the channel.

I was following the balance-transfer example, so after channel creation, peers need to be joined to that channel.

There are 2 peers which joined the channel ["peer0.org1.example.com", "peer0.org1.example.com"], so when I am instantiating the chaincode it is creating 2 docker images of chaincode 

dev-peer0.org1.example.com-chaincode-v0  
dev-peer1.org1.example.com-chaincode-v0

What these 2 images really mean?
Isn't initializing the chaincode means for the channel?
Or channel initialize it on all the peers who joined it?
Where actually this initialization is happening?

Thanks!

Shubham Chadokar
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2 Answers2

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Thanks to @PaulO'Mahony and @kajuken for the resources and explanation.
Following are the summary of my doubts:

  1. A chaincode runs in a Docker container that is associated with any peer that needs to interact with it.
  2. Chaincode is installed on a peer, then instantiated on a channel.

All members that want to submit transactions or read data by using a chaincode need to install the chaincode on their peer.

  1. Instantiation will input the initial data used by the chaincode, and then start the chaincode containers on peers joined to the channel with the chaincode installed.

Note that only one network member needs to instantiate a chaincode. If a peer with a chaincode installed joins a channel where it has already been instantiated, the chaincode container will start automatically.

a chaincode is installed onto the file system of every peer that joins a channel, the chaincode must then be instantiated on the channel so that peers can interact with the ledger via the chaincode container. The instantiation performs any necessary initialization of the chaincode. This will often involve setting the key value pairs that comprise a chaincode's initial world state.

  1. A peer can the install the chaincode once, and then use the same chaincode container on any channel where it has been instantiated.

References:
install and instantiate the chaincode
instantiate the chaincode

Community
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Shubham Chadokar
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What these 2 images really mean? Isn't initializing the chaincode means for the channel?

Yes and no. Every peer needs the same version of the chaincode installed on itself since everybody needs to be able to execute and verify incoming queries/invokes. So there are 2 steps to do.

  1. install the chaincode on every peer on the channel
  2. instantiate the chaincode on the channel

Where actually this initialization is happening?

So the instantiating of chaincode is happening last after every peer has "knowledge" of the chaincode and it can be verified.

kajuken
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  • sorry I think you didn't understood the question. Installation is for peers to contribute in invoking the chaincode. But instantiation give knowledge to channel about which chaincode version it has to call when it is invoked. When you instantiate it create 2 docker images 1 for/of each peer who joined the channel. This is the step question is all about. Why there are multiple images? – Shubham Chadokar Mar 05 '19 at 11:31
  • Oh well then i think we are talking past each other. Each peer has its own ChainCode image to protect itself. Failing or malicious code can be executed in an isolated environment and does not affect the peer. Every transactions/proposal to the peer will be directed to that image. – kajuken Mar 05 '19 at 11:50
  • the answer to your questions are in the Fabric docs -> https://hyperledger-fabric.readthedocs.io/en/release-1.4/chaincode4noah.html?highlight=instantiate (by the way they're instantiated container instances, not docker images). A chaincode runs in a Docker container that is associated with any peer that needs to interact with it. In general, a chaincode has to be installed only on those peers through which the chaincode needs to be accessed from. In particular, the chaincode must be installed on any peer receiving endorsement requests for that chaincode. Peers can be in different orgs. – Paul O'Mahony Mar 05 '19 at 11:51
  • @PaulO'Mahony so what i understood is, channel instantiate the chaincode on peers in which chaincode is installed not on the channel? am i correct? so when a peer from different org join channel and install chaincode so what will that time? as instantiate runs only once per chaincode. – Shubham Chadokar Mar 05 '19 at 12:00
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    @ShubhamChadokar [This](https://cloud.ibm.com/docs/services/blockchain/howto?topic=blockchain-install-instantiate-chaincode&locale=en#install-instantiate-chaincode) will help you on the first question. "[...]Peers may want to join multiple channels that use the same chaincode, but with different sets of network members able to access the data. A peer can the install the chaincode once, and then use the same chaincode container on any channel where it has been instantiated. This lightweight approach saves compute and storage space, and helps you scale your network." – kajuken Mar 05 '19 at 12:12
  • @kajuken thanks for the link it really helped and resolved my doubts. – Shubham Chadokar Mar 06 '19 at 06:13