High Level Summary of APIC Upgrades and Downgrades
When performing an upgrade or downgrade of an APIC cluster, there is a certain sequence of events that occur to allow for the upgrade or downgrade of each APIC separately, along with ensuring that the data on the upgraded or downgraded APIC will be compatible with the target image. Most of these events happen in the background, so it’s important to understand what you should expect to see when you trigger an upgrade or downgrade of the APIC cluster.
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Image is uploaded to the firmware repository. The image is synced to all APIC cluster members.
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Upgrade or downgrade is triggered to a specific target version.
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Each APIC in the cluster goes through the process to install the new image in the first grub partition. This happens in parallel to speed up the upgrade or downgrade process.
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Once the image installation is completed, each APIC takes its turn to go through a data conversion process of the database files in a sequential order. When this occurs, the following events happen:
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The Data Management Engine (DME) processes shut down. This includes the nginx web server which services all API requests. Because of this, you will lose access to the UI/API, as well as any other backend application that runs on that APIC.
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The database files are converted from the initial version to the target version. The amount of time this takes is dependent on the size of the configuration deployed on the ACI fabric. Because of this, the total time to complete the conversion will vary between deployments.
When your source version is APIC release 6.0(3) or newer, the database conversion process has been enhanced and users may notice a shorter wait time for this process compared to the previous releases.
Note
It’s critical that there is no disruptive action taken to the APIC at this stage, as it could result in data loss or partial configuration if this stage does not complete successfully. See Guidelines and Limitations for Upgrading or Downgrading for more information.
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The APIC will then reload after the database conversion process has completed successfully and will boot up on the version of software defined in the target version.
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After the APIC that performed the reload comes back online, the sequence of events outlined in Step 4 happen to the next APIC in the cluster. This process repeats itself until all members of the cluster have been upgraded or downgraded.