Scalability

Definition

Scalability refers to the size of the solution. This size can
be related to the entire solution or to a specific
component(s) of it.

When designing a solution and hybrid networking connectivity
in particular, you need to consider the current size, as well
as the anticipated growth of the solution. This growth can be
either an organic growth of a solution, or might be related to
a merger and acquisition type of scenarios, where the size can
be increased dramatically within a short period of time. In
the context of a hybrid network connectivity design,
scalability refers to the design’s ability to support the
current and future requirements related to:

• Number of on-premises sites to be connected to AWS

• Number of AWS Regions to be used

• Number of Amazon VPCs within each Region

• Number of routes to be exchanged

• Bandwidth requirements

Impact on the design

The understanding of the current and the anticipated future
scale requirements is critical, because it will influence the
decision with regard to the optimal connectivity option
selection and design. To be able to analyze the connectivity
options in relation to the targeted solution scale, first we
need to identify what are the influencing factors that need to
be considered as part of the scale analysis when selecting and
designing a hybrid connectivity solution architecture. The
following list summarizes the key elements that impact the
design decision regarding scale:

• Number of Amazon VPCs –
  The number of VPCs that need to be connected to an
  on-premises site(s). Different connectivity options have
  limits that need to be taken into consideration at the
  decision-making stage.

• Number of AWS Regions to be
  used – For multi-Region architectures, it’s
  important to identify the required number of Regions to
  connect or anticipated to be connected to an on-premises
  site. This helps to minimize unexpected limitations in
  terms of the supported number of Regions to connect to,
  and major design changes.

• Number of on-premises sites to be
  connected to AWS –
  The number of sites to
  be connected to AWS impacts the decision of how many
  connections are required to be set up that will influence
  the entire hybrid connectivity design. From a logical
  design point of view, this also has implications on the
  routing complexity, such as number of BGP peering
  sessions.

• The number of advertised
  prefixes – This element is related to the
  control plane aspect (IP routing). Because different AWS
  services have different quotas, the required scale of IP
  routing information (routes) to be advertised to or from
  AWS can influence the design decision.

• Bandwidth – In the
  context of scalability, this refers to the ability of a
  connection or link to support increased bandwidth
  capacity. For example, from 1G to 10G over same fiber
  link, or more VPN bandwidth capacity by adding more VPN
  Tunnels.

Note

Depending on the targeted solution architecture, not all of the preceding elements
need to be taken into consideration. However, they can serve as the foundational
elements to identify scalability requirements of most common hybrid network solutions.
This whitepaper focuses on the hybrid connectivity selection and design. Therefore, the
preceding scale elements are mainly focused on the hybrid connectivity selection and
design. Nevertheless, we recommend that you look at the big picture. Therefore, we
further recommend that you expand the scale consideration of the hybrid connectivity to
the VPC’s networking architecture. For more information about the selected hybrid
connectivity design, see the AWS whitepaper Building a Scalable and Secure Multi-VPC AWS Network Infrastructure.

Requirement definition

• What is the current or anticipated number of VPCs which
  require connectivity to on-premises site(s)?

• Are these VPCs deployed in a single AWS Region or multiple
  Regions?

• How many on-premises sites need to be connected to AWS?

• How many customer gateway devices (e.g. routers) you have
  per site that need to connect to AWS?

• How many routes are expected to be advertised to Amazon VPCs as well as the number of expected routes to be
  received from AWS side?

• Is there a requirement to increase bandwidth to AWS
  overtime?

Technical solutions

To address scale requirements as part of the hybrid
connectivity design, ideally it should be combined with the
connectivity model design. Therefore,
Connectivity models
incorporate scale as part of the targeted connectivity model design.

The following are recommended best practices to minimize scale
complexity of hybrid network connectivity design:

• Use route summarization to reduce the number of routes
  advertised to and received from AWS. This indicates that a
  structured IP addressing scheme needs to be planned ahead
  of time that ultimately will simplify the use of route
  summarization. You should design this with traffic
  engineering in mind. For more information, see
  Traffic engineering.

• Minimize the number of BGP peering sessions by using DXGW
  with VGW or AWS Transit Gateway, where a single BGP
  session can provide connectivity to multiple VPCs.