This image shows two Endeca MDEX distribution groups residing in different fault domains. As the index is updated in one fault domain, user requests are made only to the other fault domain. The image contains three functional tiers:

• Tier 1: Contains a box labeled Oracle Commerce that contains the text Endeca EAC/XM. An arrow labeled Index Update connects to fault domain 1 in tier 2.
• Tier 2: Contains two boxes, one labeled fault domain 1 and the other labeled fault domain 2. Fault domain 1 shows Endeca MDEX distribution group 1, version 1 updating to version 2. Fault domain 2 contains Endeca MDEX distribution group 2, version 1.
• Tier 3: Contains a box labeled Oracle Commerce that contains the text ATG. A user request originating from ATG connects to fault domain 2 in tier 2 (no user requests are sent to fault domain 1).