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containers often get their own IP address
wordpress container 1: I’m running WordPress at 172.17.2.3:8080!
wordpress container 2: I’m using 172.17.0.49:8080!
containers use private IP addresses
These are reserved for private networks (RFC 1918).
This is because they’re not directly on the public internet.
for a packet to get to the right place, it needs a route
packet 172.16.2.3: hi! I’m here!
router, represented by a box with a nonplussed expression: I don’t have any entry
matching 172.16.2.3 in my route table, sorry!
inside the same computer, you’ll have the right routes
same computer:
$ curl 172.16.2.3:8080
<html>....
different computer:
$ curl 172.16.2.3:8080
.... no reply ....
distributing the right routes is complicated
box with a smiley face: a new container started, 10.2.73.4 should go to X computer now
route table, also represented by a box with a smiley face, thinking: wow these things change a lot
cloud providers have systems to make container IPs work
In AWS, this is called an “elastic network interface” route table