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Introduce EXPOSE

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This commit is contained in:
Jerome Petazzoni
2018-04-02 00:10:45 -05:00
parent deaee0dc82
commit b21185dde7
1 changed files with 31 additions and 6 deletions
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37
slides/intro/Container_Networking_Basics.md
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@@ -49,14 +49,14 @@ We will use `docker ps`:
```bash
$ docker ps
CONTAINER ID IMAGE ... PORTS ...
e40ffb406c9e nginx ... 0.0.0.0:32769->80/tcp, 0.0.0.0:32768->443/tcp ...
CONTAINER ID IMAGE ... PORTS ...
e40ffb406c9e nginx ... 0.0.0.0:32768->80/tcp ...
```
* The web server is running on ports 80 and 443 inside the container.
* The web server is running on port 80 inside the container.
* Those ports are mapped to ports 32769 and 32768 on our Docker host.
* This port is mapped to port 32768 on our Docker host.
We will explain the whys and hows of this port mapping.
@@ -81,7 +81,7 @@ Make sure to use the right port number if it is different
from the example below:
```bash
$ curl localhost:32769
$ curl localhost:32768
<!DOCTYPE html>
<html>
<head>
@@ -91,6 +91,31 @@ $ curl localhost:32769
---
## How does Docker know which port to map?
* There is metadata in the image telling "this image has something on port 80".
* We can see that metadata with `docker inspect`:
```bash
$ docker inspect nginx --format {{.Config.ExposedPorts}}
map[80/tcp:{}]
```
* This metadata was set in the Dockerfile, with the `EXPOSE` keyword.
* We can see that with `docker history`:
```bash
$ docker history nginx
IMAGE CREATED CREATED BY
7f70b30f2cc6 11 days ago /bin/sh -c #(nop) CMD ["nginx" "-g" "…
<missing> 11 days ago /bin/sh -c #(nop) STOPSIGNAL [SIGTERM]
<missing> 11 days ago /bin/sh -c #(nop) EXPOSE 80/tcp
```
---
## Why are we mapping ports?
* We are out of IPv4 addresses.
@@ -113,7 +138,7 @@ There is a command to help us:
```bash
$ docker port <containerID> 80
32769
32768
```
---