Deployment and Proxy Placement
Why this matters: every previous lesson assumed edges exist in the right places. This is where that assumption gets paid for — and placement decisions are what separate Akamai's approach from Google's.
Key takeaway
Before installing a CDN facility you must determine the optimal number of proxy servers and their best locations. Proxies should be placed in network locations with high connectivity.
The two questions
- What are the best locations to install proxy servers?
- How many proxy servers are required?
Two placement strategies
| Strategy | Where | Character |
|---|---|---|
| On-premises | Smaller data centers near major IXPs (internet exchange points) | Fewer, larger facilities at network crossroads |
| Off-premises | Proxies placed directly inside ISP networks | Many, smaller footprints — content one hop from users |
Caching static content such as movies at ISP edge locations is feasible. But services with rapidly growing datasets face a harder question: which content to cache near users at all.
Split TCP
One approach for long-haul delivery is to split TCP.
Client TCP connections terminate at edge infrastructure near IXPs. That edge then forwards traffic to central data centers over persistent, low-latency connections configured with large TCP window sizes.
This reduces client-perceived latency by avoiding the initial TCP three-way handshake and slow-start phases over long distances. Since the round-trip delay to the local IXP is low, the handshake overhead is negligible.
Additionally, predictive push strategies help determine which content to proactively move closer to users — pushing based on forecast demand rather than observed requests.
Choosing locations and counts
Placement decisions rely on performance measurements. Tools such as ProxyTeller calculate optimal locations and server counts based on hit ratio, bandwidth, and latency. Other algorithms — greedy, random, and hotspot strategies — are also used.
Why ISPs want the boxes
Placement inside an ISP is a negotiation, and it helps to know the other side's incentives. An ISP benefits because:
| Benefit | Detail |
|---|---|
| Lower transit costs | A CDN node cuts the external bandwidth ISPs need and pay for; SLAs with proxy providers may benefit them economically |
| Happier customers | It improves responsiveness for the ISP's customers, giving a competitive advantage over ISPs without a CDN node |
| Less core traffic | Bringing content closer to users reduces data on the internet core |
Key takeaway
Place edges where connectivity is dense — at IXPs for volatile or vast catalogues, inside ISPs for large but stable ones. And remember that placement improves delivery through transport effects like split TCP, not caching alone.
Interview signal by level
| Level | What a strong answer sounds like |
|---|---|
| L4 | "We put edge servers in different regions." |
| L5 | Knows the two options: "either near IXPs or directly inside ISP networks — inside the ISP puts content about one hop from users." |
| Staff+ | Ties placement to content shape and incentives: "stable catalogues go inside ISPs like Akamai and Netflix; volatile ones sit near IXPs like Google, because you'd otherwise invalidate thousands of footprints constantly. And ISPs take the box because it cuts their transit bill — the incentives align." |
Next: whether to run any of this yourself.