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© Rakhesh Sasidharan

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Quick note to self on NSX Load Balancing

Inline mode == Transparent mode (the latter is the terminology in the UI).

In this mode the load balancer is usually the default gateway for the servers it load balances. Traffic comes to the load balancer, it sends to the appropriate server (after changing the destination IP of the packet – hence DNAT), and replies come to it as it is the default gateway for the server. Note that as far as the destination server is concerned the source IP address is not the load balancer but the client who made the request. Thus the destination server knows who is making the request.

When the load balancer replies to the client who made the request it changes the source IP of the reply from the selected server to its own IP (hence SNAT when replying only).

One-Armed mode == Proxy mode

In this mode the load balancer is not the default gateway. The servers it load balance don’t have any changes required to be made to them. The load balancer does a DNAT as before, but also changes the source IP to be itself rather than the client (hence SNAT). When the selected server replies this time, it thinks the source is the load balancer and so replies to it rather than the client. Thus there’s no changes required on the server side. Because of this though, the server doesn’t know who made the request. All requests appear to come from the load balancer (unless you use some headers to capture the info).

As before, when the load balancer replies to the client who made the request it changes the source IP of the reply from the selected server to its own IP (hence SNAT when replying too).

You set the inline/ transparent vs. one-armed/ proxy mode per pool.

To have load balancing in NSX you need to deploy an ESG (Edge Services Gateway). I don’t know why, but I always associated an ESG with just external routing so it took me by surprise (and still does) when I think I need to deploy an ESG for load balancing, DHCP, and other edge- sort of services (VPN, routing, etc). I guess the point to remember is that it’s not just a gateway – it’s an edge services gateway. :)

Anyways, feel free to deploy as many ESGs as you feel like. You can have one huge ESG that takes care of all your load balancing needs, or you can have multiple small ones and hand over control to the responsible teams.

This is a good starting point doc from VMware.

You can have L4 and L7 load balancing. If you need only L4 (i.e. TCP, UDP, port number) the UI calls it acceleration. It’s a global configuration, on the ESG instance itself, so bear that in mind.

If you enable acceleration on an ESG, you have to also enable it per virtual server.

L4 load balancing is packet based (obviously, coz it doesn’t need to worry about the application as such). L7 load balancing is socket based. Quoting from this doc (highlight mine):

Packet-based load balancing is implemented on the TCP and UDP layer. Packet-based load balancing does not stop the connection or buffer the whole request, it sends the packet directly to the selected server after manipulating the packet. TCP and UDP sessions are maintained in the load balancer so that packets for a single session are directed to the same server. You can select Acceleration Enable in both the global configuration and relevant virtual server configuration to enable packet-based load balancing.

Socket-based load balancing is implemented on top of the socket interface. Two connections are established for a single request, a client-facing connection and a server-facing connection. The server-facing connection is established after server selection. For HTTP socket-based implementation, the whole request is received before sending to the selected server with optional L7 manipulation. For HTTPS socket-based implementation, authentication information is exchanged either on the client-facing connection or on the server-facing connection. Socket-based load balancing is the default mode for TCP, HTTP, and HTTPS virtual servers.

Also worth noting:

The L4 VIP (“acceleration enabled” in the VIP configuration and no L7 setting such as AppProfile with cookie persistence or SSL-Offload) is processed before the edge firewall, and no edge firewall rule is required to reach the VIP. However, if the VIP is using a pool in non-transparent mode, the edge firewall must be enabled (to allow the auto-created SNAT rule).

The L7 HTTP/HTTPS VIPs (“acceleration disabled” or L7 setting such as AppProfile with cookie persistence or SSL-Offload) are processed after the edge firewall, and require an edge firewall allow rule to reach the VIP.

Application Profiles define common application behaviors client SSL, server SSL, x-forwarded-for, and persistence. These can be reused across virtual server and is mandatory when defining a virtual server. This is also where you can do HTTP redirects.

Quick note to self on NSX Load Balancing by rakhesh is licensed under a Creative Commons Attribution 4.0 International License.