As Kronicklez already mentions below an ESI-LAG will indeed require EVPN-VXLAN (technically they are EVPN-LAGs, and an ESI is used as an identifier in those to signal between the nodes)
Basically the (high level) concept of an ESI-LAG is that it's sort of an MC-LAG but instead of using a dedicated ICCP/ICL connection to sync between the nodes it uses an EVPN-VXLAN tunnel between these nodes instead (eliminating the need for these dedicated ICCP/ICL connections).
There are almost certainly some more differences at a more detailed level, but this is looking at it from a more high level conceptual overview.
So in your example case you'd either need to set up an EVPN-VXLAN fabric between the devices in order to be able to use ESI-LAG, or otherwise you'll need to look into MC-LAG and the prerequisites for that (primary among those being the dedicated ICCP and ICL links between the switches)
Ethernet Segment Identifiers, ESI Types, and LACP in EVPN LAGs - TechLibrary - Juniper Networks
Understanding Multichassis Link Aggregation Groups | Junos OS | Juniper Networks
Sent: 05-08-2023 23:42
Subject: ESI-Lag Question
Hi, Basic question but couldn't find answer anywhere so posting here. Does ESI-LAG works only in VXLAN/EVPN environment? I'm trying to connect two standalone QFX's to Palo, a physical link from each QFX to Active/Passive Palo setup and bundle them on Palo as ae interface and enable LACP (Except this basic setup there are not other configs on device). As per the documentations, I either need MLAG or ESI-LAG and there is no plan to connect QFX together as of now so I think that eliminates MLAG setup. Do ESI Lag works in my case or ESI-LAG needs VXLAN/EVPN setu
p enabled as well? Any suggestions or recommendations? Thank you!!