What is a Hard Fork and Upgrade and how does it differ from Upgrade
To apply with newer software releases to your Environment, Kaleido provides the ability to perform a Rolling Upgrade that upgrades runtimes one at a time, thus ensuring continuous availability of your Blockchain Environment. Over time, newer versions of Ethereum introduce support for additional EIPs or Chain Configuration which are essentially upgrades to the protocol running on the runtime. In order to synchronize the protocol version running across the entire network, each EIP is configured with a Block Number at which it is made active by the runtime software. Kaleido provides the ability to add such additional EIPs using a Hard Fork operation, which is available in Settings panel of your Environment. Hard Fork does not change the runtime release of Kaleido software running in your Environment and only schedules any available EIPs in that release. Hard Fork results in a simultaneous restart of all nodes running in the environment and hence involves a slight downtime for your network.
In release 1.0.35, we added support for Quorum 2.7. In order to migrate your existing Environment (see references section below for a link to the quorum migration guidance) from Quorum 2.5 to Quorum 2.7, all nodes must be upgraded and every node's chain configuration must be updated with the new EIPs - PetersburgBlock and IstanbulBlock. To achieve this, the environment must undergo a Hard Fork to add the new EIPs available in Quorum 2.7 and at the same time upgrade the runtime version to Quorum 2.7. This mechanism is now made possible with a new Hard Fork and Upgrade option in the Environment Settings panel. Note that this option is automatically enabled when it relevant. If this option is visible, you will also notice that the Upgrade option is not visible, because a rolling upgrade is not a supported procedure to upgrade to Quorum 2.7 from earlier versions.