Push vs Pull CDN

You already know a CDN keeps copies of your files (images, videos, CSS) on servers around the world, so users get them from a nearby place instead of your far-away main server. But that raises a practical question:

• How does the CDN actually get your files in the first place?

There are two answers, and they’re opposite approaches. Either you push the files to the CDN yourself ahead of time, or the CDN pulls them from your server the first time someone asks. Each fits a different situation. Let’s walk through both.

🎯 First, the Origin Server

One quick term before we start. Your main server, the one that holds the original copy of everything, is called the origin server. The CDN’s job is to keep copies of the origin’s files closer to users. Push and pull are just two ways those copies get from the origin to the CDN.

📤 Push CDN

With a push CDN, you upload your files to the CDN yourself, ahead of time. You decide what goes there and when. The CDN just stores what you gave it and serves it.

How it goes:

• You upload your files to the CDN whenever you publish or update them.
• The CDN holds those copies and serves them to users, fast, from the start.
• Nothing is fetched on demand. It’s all there in advance because you put it there.

The trade-offs:

• Good: even the very first user gets it fast, since the file is already on the CDN.
• Good: you control exactly what’s stored and when it updates.
• Bad: more work for you. You have to upload, and re-upload when files change.
• Bad: it can waste space storing files that few people ever request.

📥 Pull CDN

With a pull CDN, you don’t upload anything ahead of time. The CDN fetches a file from your origin server the first time a user asks for it, then keeps a copy for the next users.

How it goes:

• A user asks the CDN for a file. The CDN doesn’t have it yet (a miss).
• So the CDN pulls it from your origin server, hands it to the user, and saves a copy.
• The next users who want that file get the saved copy, fast.

The trade-offs:

• Good: almost no work for you. You just point the CDN at your origin and it handles the rest.
• Good: it only stores files people actually request, so no wasted space.
• Bad: the very first user for each file is slow, because the CDN has to fetch it from the origin that one time.

Reading that: the first request triggers a pull from the origin, then everyone after gets the cached copy quickly.

📊 Push vs Pull

Here’s the side-by-side.

🧭 When to Use Which

A simple way to choose:

• You have a small amount of large content that doesn’t change much, like big download files or a few videos? Push. Upload once, every user gets it fast.
• You have lots of content that changes often, like a busy website’s images? Pull. Let the CDN fetch what’s needed, and don’t manage uploads yourself.

Most websites use pull, because it’s so much less work and it naturally keeps only the popular files. Push shows up for special cases where you want full control or guaranteed-fast first delivery.

⚠️ Common Mistakes and Misconceptions

A few things to keep straight:

• “Pull CDN means every request is slow.” No, only the very first request for each file. After that, the copy is cached and fast for everyone else.
• “Push CDN is always better because it’s pre-loaded.” Not always. It’s more work and can waste space on files nobody requests. For big, changing sites, pull is easier.
• “The CDN replaces your origin server.” It doesn’t. The origin still holds the original files. The CDN just keeps copies closer to users.

🧩 What You’ve Learned

Nice work. Here’s the recap:

• ✅ Your origin server holds the original files; the CDN keeps copies closer to users.
• ✅ Push CDN: you upload content ahead of time, so even the first user is fast, but it’s more work.
• ✅ Pull CDN: the CDN fetches a file on first request and caches it, so only the first user is slow.
• ✅ Use push for few large rarely-changing files; use pull for lots of often-changing content.

🧠

Check Your Knowledge

Test what you learned. Pick an answer for each question, then click Check.

1. 1

   In a pull CDN, when does the CDN get a file?

   You upload it ahead of time It fetches the file from the origin the first time a user asks It never gets the file Every night automatically
   Check

   Why: A pull CDN fetches a file from the origin on the first request (a miss), then caches it for later users.

2. 2

   What is the main downside of a pull CDN?

   Every request is slow The very first user for each file is slow, since it's fetched once It needs lots of manual uploads It can't cache anything
   Check

   Why: Only the first request for each file is slow, because the CDN must fetch it from the origin that one time. Later requests are fast.

3. 3

   When is a push CDN a good fit?

   Lots of files that change all the time A few large files that rarely change, where you want fast first delivery When you want the least possible work When you have no origin server
   Check

   Why: Push suits a small amount of large, rarely-changing content. You upload once and even the first user gets it fast.

4. 4

   What is the origin server?

   The user's phone Your main server that holds the original copy of the files The closest CDN node The load balancer
   Check

   Why: The origin server holds the original files. The CDN keeps copies of them closer to users; it doesn't replace the origin.

Score: 0 / 4 Reset

🚀 What’s Next?

You know how content gets onto a CDN. Let’s go deeper on keeping it fresh.

• CDN Caching Strategies covers how long copies live and when they refresh.
• CDN Explained is the foundation this builds on.

Get these down and you’ll understand how the world’s content stays close and fast.