What is difference b/w 'Transit GW', 'Direct Connect GW' and 'Direct Connection'?

Question

I am new to AWS and always find it confusing to differentiate b/w 'Transit GW', 'Direct Connect GW' and 'Direct Connection'?
Can someone please help explain the difference using an example?
- Many Thanks!

Accepted Answer

**Transit GW**  
As described in the documentation, Transit GW is a service that serves as a hub for communication between on-premises and VPCs.  
DirectConnect can also connect to on-premises, but the difference is that it can be configured to intercommunicate with multiple VPCs and on-premises.  
https://docs.aws.amazon.com/vpc/latest/tgw/what-is-transit-gateway.html

**Direct Connect GW**  
DirectConnect GW can be used to connect on-premises to multiple VPCs.  
As a comparison with Transit GW, Direct Connect GW cannot intercommunicate with multiple VPCs.  
Use Transit GW when communicating with on-premises or VPC like a hub.  
https://docs.aws.amazon.com/directconnect/latest/UserGuide/direct-connect-gateways-intro.html

**DirectConnect**  
DirectConnect is a leased line connection service.  
Transit GW can also communicate from on-premises to AWS, but this one uses Site to Site VPN (IPSec VPN).  
If you want to communicate with multiple VPCs via DirectConnect, use Direct Connect GW.  
Also, if you want to achieve hub-like intercommunication with multiple VPCs, we recommend using a Transit GW instead of a DirectConnect GW tied to DirectConnect.  
https://docs.aws.amazon.com/directconnect/latest/UserGuide/Welcome.html

Answer

Direct Connect is a private link between your VPCs and on-prem that doesn't go over the internet.

Transit Gateway is a kind of hub where you can join subnets together and control routing between them.  So you can link up VPCs together and with on-prem via site-to-site VPNs and Direct Connect for example.

Direct Connect Gateway is a helpful network piece for mediating and aggregating connections.  It can simplify on-prem connectivity with many VPCs - no need to set up a BGP session (VIF) for every single VPC, so expands the number of VPCs that a Direct Connect connection supports.  Also it lets you:
* reach AWS resources in other regions via a single DX and AWS global backbone instead of having to sort your own global WAN and have a DX in another part of the world
* Share a direct connect link with up to 3 Transit Gateways across accounts
* Consolidate a lot of on-prem branch offices connecting to your AWS infrastructure; they don't need to all independently hook up to all the VPCs.

Answer

this is a great resource explaining various VPC connectivity options with supporting images 
https://docs.aws.amazon.com/whitepapers/latest/aws-vpc-connectivity-options/network-to-amazon-vpc-connectivity-options.html

What is difference b/w 'Transit GW', 'Direct Connect GW' and 'Direct Connection'?

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