Chaincode for Operators

What is Chaincode?

Chaincode is a program, written in Go, Node.js, or Java that implements a prescribed interface. Chaincode runs in a secured Docker container isolated from the endorsing peer process. Chaincode initializes and manages ledger state through transactions submitted by applications.

A chaincode typically handles business logic agreed to by members of the network, so it may be considered as a “smart contract”. Ledger updates created by a chaincode are scoped exclusively to that chaincode and can’t be accessed directly by another chaincode. However, within the same network, given the appropriate permission a chaincode may invoke another chaincode to access its state.

In the following sections, we will explore chaincode through the eyes of a blockchain network operator rather than an application developer. Chaincode operators can use this tutorial to learn how to use the Fabric chainode lifecycle to deploy and manage chaincode on their network.

Chaincode lifecycle

The Fabric chaincode lifecycle is a process that allows multiple organizations to agree on how a chaincode will be operated before it can be used on a channel. The tutorial will discuss how a chaincode operator would use the Fabric lifecycle to perform the following tasks:

If you are upgrading from a v1.4.x network and need to edit your channel configurations to enable the new lifecycle, check out Enabling the new chaincode lifecycle.

Install and define a chaincode

Fabric chaincode lifecycle requires that organizations agree to the parameters that define a chaincode, such as name, version, and the chaincode endorsement policy. Channel members come to agreement using the following four steps. Not every organization on a channel needs to complete each step.

  1. Package the chaincode: This step can be completed by one organization or by each organization.
  2. Install the chaincode on your peers: Every organization that will use the chaincode to endorse a transaction or query the ledger needs to complete this step.
  3. Approve a chaincode definition for your organization: Every organization that will use the chaincode needs to complete this step. The chaincode definition needs to be approved by a sufficient number of organizations to satisfy the channel’s LifecycleEndorsment policy (a majority, by default) before the chaincode can be started on the channel.
  4. Commit the chaincode definition to the channel: The commit transaction needs to be submitted by one organization once the required number of organizations on the channel have approved. The submitter first collects endorsements from enough peers of the organizations that have approved, and then submits the transaction to commit the chaincode definition.

This tutorial provides a detailed overview of the operations of the Fabric chaincode lifecycle rather than the specific commands. To learn more about how to use the Fabric lifecycle using the Peer CLI, see Install and define a chaincode in the Building your First Network Tutorial or the peer lifecycle command reference. To learn more about how to use the Fabric lifecycle using the Fabric SDK for Node.js, visit How to install and start your chaincode.

Step One: Packaging the smart contract

Chaincode needs to be packaged in a tar file before it can be installed on your peers. You can package a chaincode using the Fabric peer binaries, the Node Fabric SDK, or a third party tool such as GNU tar. When you create a chaincode package, you need to provide a chaincode package label to create a succinct and human readable description of the package.

If you use a third party tool to package the chaincode, the resulting file needs to be in the format below. The Fabric peer binaries and the Fabric SDKs will automatically create a file in this format.

  • The chaincode needs to be packaged in a tar file, ending with a .tar.gz file extension.

  • The tar file needs to contain two files (no directory): a metadata file “Chaincode-Package-Metadata.json” and another tar containing the chaincode files.

  • “Chaincode-Package-Metadata.json” contains JSON that specifies the chaincode language, code path, and package label. You can see an example of a metadata file below:

    {"Path":"github.com/chaincode/fabcar/go","Type":"golang","Label":"fabcarv1"}
    

Packaging the chaincode

The chaincode is packaged separately by Org1 and Org2. Both organizations use MYCC_1 as their package label in order to identify the package using the name and version. It is not necessary for organizations to use the same package label.

Step Two: Install the chaincode on your peers

You need to install the chaincode package on every peer that will execute and endorse transactions. Whether using the CLI or an SDK, you need to complete this step using your Peer Administrator, whose signing certificate is in the admincerts folder of your peer MSP. It is recommended that organizations only package a chaincode once, and then install the same package on every peer that belongs to their org. If a channel wants to ensure that each organization is running the same chaincode, one organization can package a chaincode and send it to other channel members out of band.

A successful install command will return a chaincode package identifier, which is the package label combined with a hash of the package. This package identifier is used to associate a chaincode package installed on your peers with a chaincode definition approved by your organization. Save the identifier for next step. You can also find the package identifier by querying the packages installed on your peer using the Peer CLI.

Installing the chaincode

A peer administrator from Org1 and Org2 installs the chaincode package MYCC_1 on the peers joined to the channel. Installing the chaincode package creates a package identifier of MYCC_1:hash.

Step Three: Approve a chaincode definition for your organization

The chaincode is governed by a chaincode definition. When channel members approve a chaincode definition, the approval acts as a vote by an organization on the chaincode parameters it accepts. These approved organization definitions allow channel members to agree on a chaincode before it can be used on a channel. The chaincode definition includes the following parameters, which need to be consistent across organizations:

  • Name: The name that applications will use when invoking the chaincode.
  • Version: A version number or value associated with a given chaincodes package. If you upgrade the chaincode binaries, you need to change your chaincode version as well.
  • Sequence: The number of times the chaincode has been defined. This value is an integer, and is used to keep track of chaincode upgrades. For example, when you first install and approve a chaincode definition, the sequence number will be 1. When you next upgrade the chaincode, the sequence number will be incremented to 2.
  • Endorsement Policy: Which organizations need to execute and validate the transaction output. The endorsement policy can be expressed as a string passed to the CLI or the SDK, or it can reference a policy in the channel config. By default, the endorsement policy is set to Channel/Application/Endorsement, which defaults to require that a majority of organizations in the channel endorse a transaction.
  • Collection Configuration: The path to a private data collection definition file associated with your chaincode. For more information about private data collections, see the Private Data architecture reference.
  • Initialization: All chaincode need to contain an Init function that is used to initialize the chaincode. By default, this function is never executed. However, you can use the chaincode definition to request that the Init function be callable. If execution of Init is requested, fabric will ensure that Init is invoked before any other function and is only invoked once.
  • ESCC/VSCC Plugins: The name of a custom endorsement or validation plugin to be used by this chaincode.

The chaincode definition also includes the Package Identifier. This is a required parameter for each organization that wants to use the chaincode. The package ID does not need to be the same for all organizations. An organization can approve a chaincode definition without installing a chaincode package or including the identifier in the definition.

Each channel member that wants to use the chaincode needs to approve a chaincode definition for their organization. This approval needs to be submitted to the ordering service, after which it is distributed to all peers. This approval needs to be submitted by your Organization Administrator, whose signing certificate is listed as an admin cert in the MSP of your organization definition. After the approval transaction has been successfully submitted, the approved definition is stored in a collection that is available to all the peers of your organization. As a result you only need to approve a chaincode for your organization once, even if you have multiple peers.

Approving the chaincode definition

An organization administrator from Org1 and Org2 approve the chaincode definition of MYCC for their organization. The chaincode definition includes the chaincode name, version, and the endorsement policy, among other fields. Since both organizations will use the chaincode to endorse transactions, the approved definitions for both organizations need to include the packageID.

Step Four: Commit the chaincode definition to the channel

Once a sufficient number of channel members have approved a chaincode definition, one organization can commit the definition to the channel. You can use the checkcommitreadiness command to check whether committing the chaincode definition should be successful based on which channel members have approved a definition before committing it to the channel using the peer CLI. The commit transaction proposal is first sent to the peers of channel members, who query the chaincode definition approved for their organizations and endorse the definition if their organization has approved it. The transaction is then submitted to the ordering service, which then commits the chaincode definition to the channel. The commit definition transaction needs to be submitted as the Organization Administrator, whose signing certificate is listed as an admin cert in the MSP of your organization definition.

The number of organizations that need to approve a definition before it can be successfully committed to the channel is governed by the Channel/Application/LifecycleEndorsement policy. By default, this policy requires that a majority of organizations in the channel endorse the transaction. The LifecycleEndorsement policy is separate from the chaincode endorsement policy. For example, even if a chaincode endorsement policy only requires signatures from one or two organizations, a majority of channel members still need to approve the chaincode definition according to the default policy. When committing a channel definition, you need to target enough peer organizations in the channel to satisfy your LifecycleEndorsement policy.

You can also set the Channel/Application/LifecycleEndorsement policy to be a signature policy and explicitly specify the set of organizations on the channel that can approve a chaincode definition. This allows you to create a channel where a select number of organizations act as chaincode administrators and govern the business logic used by the channel. You can also use a signature policy if your channel has a large number Idemix organizations, which cannot approve chaincode definitions or endorse chaincode and may prevent the channel from reaching a majority as a result.

Committing the chaincode definition to the channel

One organization administrator from Org1 or Org2 commits the chaincode definition to the channel. The definition on the channel does not include the packageID.

An organization can approve a chaincode definition without installing the chaincode package. If an organization does not need to use the chaincode, they can approve a chaincode definition without a package identifier to ensure that the Lifecycle Endorsement policy is satisfied.

After the chaincode definition has been committed to the channel, channel members can start using the chaincode. The first invoke of the chaincode will start the chaincode containers on all of the peers targeted by the transaction proposal, as long as those peers have installed the chaincode package. You can use the chaincode definition to require the invocation of the Init function to start the chaincode. Otherwise, a channel member can start the chaincode container by invoking any transaction in the chaincode. The first invoke, whether of an Init function or other transaction, is subject to the chaincode endorsement policy. It may take a few minutes for the chaincode container to start.

Starting the chaincode on the channel

Once MYCC is defined on the channel, Org1 and Org2 can start using the chaincode. The first invoke of the chaincode on each peer starts the chaincode container on that peer.

Upgrade a chaincode

You can upgrade a chaincode using the same Fabric lifecycle process as you used to install and start the chainocode. You can upgrade the chaincode binaries, or only update the chaincode policies. Follow these steps to upgrade a chaincode:

  1. Repackage the chaincode: You only need to complete this step if you are upgrading the chaincode binaries.

    Re-package the chaincode package

Org1 and Org2 upgrade the chaincode binaries and repackage the chaincode. Both organizations use a different package label.

  1. Install the new chaincode package on your peers: Once again, you only need to complete this step if you are upgrading the chaincode binaries. Installing the new chaincode package will generate a package ID, which you will need to pass to the new chaincode definition. You also need to change the chaincode version.

    Re-install the chaincode package

Org1 and Org2 install the new package on their peers. The installation creates a new packageID.

  1. Approve a new chaincode definition: If you are upgrading the chaincode binaries, you need to update the chaincode version and the package ID in the chaincode definition. You can also update your chaincode endorsement policy without having to repackage your chaincode binaries. Channel members simply need to approve a definition with the new policy. The new definition needs to increment the sequence variable in the definition by one.

    Approve a new chaincode definition

Organization administrators from Org1 and Org2 approve the new chaincode definition for their respective organizations. The new definition references the new packageID and changes the chaincode version. Since this is the first update of the chaincode, the sequence is incremented from one to two.

  1. Commit the definition to the channel: When a sufficient number of channel members have approved the new chaincode definition, one organization can commit the new definition to upgrade the chaincode definition to the channel. There is no separate upgrade command as part of the lifecycle process.

    Commit the new definition to the channel

An organization administrator from Org1 or Org2 commits the new chaincode definition to the channel. The chaincode containers are still running the old chaincode.

  1. Upgrade the chaincode container: If you updated the chaincode definition without upgrading the chaincode package, you do not need to upgrade the chaincode container. If you did upgrade the chaincode binaries, a new invoke will upgrade the chaincode container. If you requested the execution of the Init function in the chaincode definition, you need to upgrade the chaincode container by invoking the Init function again after the new definition is successfully committed.

    Upgrade the chaincode

Once the new definition has been committed to the channel, the next invoke on each peer will automatically start the new chaincode container.

The Fabric chaincode lifecycle uses the sequence in the chaincode definition to keep track of upgrades. All channel members need to increment the sequence number by one and approve a new definition to upgrade the chaincode. The version parameter is used to track the chaincode binaries, and needs to be changed only when you upgrade the chaincode binaries.

Deployment scenarios

The following examples illustrate how you can use the Fabric chaincode lifecycle to manage channels and chaincode.

Joining a channel

A new organization can join a channel with a chaincode already defined, and start using the chaincode after installing the chaincode package and approving the chaincode definition that has already been committed to the channel.

Approve a chaincode definition

Org3 joins the channel and approves the same chaincode definition that was previously committed to the channel by Org1 and Org2.

After approving the chaincode definition, the new organization can start using the chaincode after the package has been installed on their peers. The definition does not need to be committed again. If the endorsement policy is set the default policy that requires endorsements from a majority of channel members, then the endorsement policy will be updated automatically to include the new organization.

Start the chaincode

The chaincode container will start after the first invoke of the chaincode on the Org3 peer.

Updating an endorsement policy

You can use the chaincode definition to update an endorsement policy without having to repackage or re-install the chaincode. Channel members can approve a chaincode definition with a new endorsement policy and commit it to the channel.

Approve new chaincode definition

Org1, Org2, and Org3 approve a new endorsement policy requiring that all three organizations endorse a transaction. They increment the definition sequence from one to two, but do not need to update the chaincode version.

The new endorsement policy will take effect after the new definition is committed to the channel. Channel members do not have to restart the chaincode container by invoking the chaincode or executing the Init function in order to update the endorsement policy.

Commit new chaincode definition

One organization commits the new chaincode definition to the channel to update the endorsement policy.

Approving a definition without installing the chaincode

You can approve a chaincode definition without installing the chaincode package. This allows you to endorse a chaincode definition before it is committed to the channel, even if you do not want to use the chaincode to endorse transactions or query the ledger. You need to approve the same parameters as other members of the channel, but not need to include the packageID as part of the chaincode definition.

Org3 does not install the chaincode

Org3 does not install the chaincode package. As a result, they do not need to provide a packageID as part of chaincode definition. However, Org3 can still endorse the definition of MYCC that has been committed to the channel.

One organization disagrees on the chaincode definition

An organization that does not approve a chaincode definition that has been committed to the channel cannot use the chaincode. Organizations that have either not approved a chaincode definition, or approved a different chaincode definition will not be able to execute the chaincode on their peers.

Org3 disagrees on the chaincode

Org3 approves a chaincode definition with a different endorsement policy than Org1 and Org2. As a result, Org3 cannot use the MYCC chaincode on the channel. However, Org1 or Org2 can still get enough endorsements to commit the definition to the channel and use the chaincode. Transactions from the chaincode will still be added to the ledger and stored on the Org3 peer. However, the Org3 will not be able to endorse transactions.

An organization can approve a new chaincode definition with any sequence number or version. This allows you to approve the definition that has been committed to the channel and start using the chaincode. You can also approve a new chaincode definition in order to correct any mistakes made in the process of approving or packaging a chaincode.

The channel does not agree on a chaincode definition

If the organizations on a channel do not agree on a chaincode definition, the definition cannot be committed to the channel. None of the channel members will be able to use the chaincode.

Majority disagree on the chaincode

Org1, Org2, and Org3 all approve different chaincode definitions. As a result, no member of the channel can get enough endorsements to commit a chaincode definition to the channel. No channel member will be able to use the chaincode.

Organizations install different chaincode packages

Each organization can use a different packageID when they approve a chaincode definition. This allows channel members to install different chaincode binaries that use the same endorsement policy and read and write to data in the same chaincode namespace.

Channel members can use this capability to install chaincode written in different languages and work with the language they are most comfortable. As long as the chaincode generates the same read-write sets, channel members using chaincode in different languages will be able to endorse transactions and commit them to the ledger. However, organizations should test that their chaincode is consistent and that they are able to generate valid endorsements before defining it on a channel in production.

Using different chaincode languages

Org1 installs a package of the MYCC chaincode written in Golang, while Org2 installs MYCC written in Java.

Organizations can also use this capability to install smart contracts that contain business logic that is specific to their organization. Each organization’s smart contract could contain additional validation that the organization requires before their peers endorse a transaction. Each organization can also write code that helps integrate the smart contract with data from their existing systems.

Using different chaincode binaries

Org1 and Org2 each install versions of the MYCC chaincode containing business logic that is specific to their organization.

Creating multiple chaincodes using one package

You can use one chaincode package to create multiple chaincode instances on a channel by approving and committing multiple chaincode definitions. Each definition needs to specify a different chaincode name. This allows you to run multiple instances of a smart contract on a channel, but have the contract be subject to different endorsement policies.

Starting multiple chaincodes

Org1 and Org2 use the MYCC_1 chaincode package to approve and commit two different chaincode definitions. As a result, both peers have two chaincode containers running on their peers. MYCC1 has an endorsement policy of 1 out of 2, while MYCC2 has an endorsement policy of 2 out of 2.

Migrate to the new Fabric lifecycle

For information about migrating to the new lifecycle, check out Considerations for getting to v2.0.

If you need to update your channel configurations to enable the new lifecycle, check out Enabling the new chaincode lifecycle.