# Make Requests from Docker Container Running on Jenkins
This post is about a specific problem I encountered where I **couldn't make any requests from my Docker container to the outside world**. It was my first time working with Jenkins Pipelines and decided to use Docker as my isolation agent.
Some facts related to my environment:
- Jenkins is running on Tomcat, not on a Docker container
- I have port redirection (80 to 8080 and 443 to 8443) using **iptables**
## Code in question
The relevant part of my Jenkinsfile is this:
```groovy
stage('build and test apps') {
failFast true
parallel {
stage('front end') {
steps {
sh 'npm install --prefix front_end/'
sh 'npm run build --prefix front_end/'
sh 'npm run test --prefix front_end/'
}
}
stage('back end') {
steps {
sh 'npm install --prefix back_end/'
sh 'npm run test --prefix back_end/'
}
}
}
}
```
## The logs
The requests needed on the `npm install` command were **failing with 403 http errors** and this log was appearing:
```text
npm ERR! Unexpected token < in JSON at position 0
npm ERR!
npm ERR!
npm ERR!
npm ERR! Authentication required
npm ERR!
npm ERR!
npm ERR!
npm ERR!
npm ERR! If you need help, you may report this error at:
npm ERR!
```
After reading the logs, the first thing I thought was: this is something related to permissions of the user running the Docker container- **tomcat** in my case -but they weren't.
After debugging for quite a while, I stumbled upon some divine light on StackOverflow. Thanks to this, I found that I was redirecting **all** port 80 and 443 trafic from **everywhere** to their corresponding 8080 and 8443 ports.
## The solution
**Alter the iptables to create a negated rule and avoid redirects from the Docker subnet**.
First, check your current iptables with this command: ```iptables -t nat -L -n --line-numbers```
```
Chain PREROUTING (policy ACCEPT)
num target prot opt source destination
1 REDIRECT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:80 redir ports 8080
2 REDIRECT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:443 redir ports 8443
3 tcp -- 0.0.0.0/0 0.0.0.0/0
4 DOCKER all -- 0.0.0.0/0 0.0.0.0/0 ADDRTYPE match dst-type LOCAL
Chain INPUT (policy ACCEPT)
num target prot opt source destination
Chain OUTPUT (policy ACCEPT)
num target prot opt source destination
1 REDIRECT tcp -- 0.0.0.0/0 127.0.0.1 tcp dpt:443 redir ports 8443
2 REDIRECT tcp -- 0.0.0.0/0 127.0.0.1 tcp dpt:80 redir ports 8080
3 DOCKER all -- 0.0.0.0/0 !127.0.0.0/8 ADDRTYPE match dst-type LOCAL
Chain POSTROUTING (policy ACCEPT)
num target prot opt source destination
1 MASQUERADE all -- 172.17.0.0/16 0.0.0.0/0
Chain DOCKER (2 references)
num target prot opt source destination
1 RETURN all -- 0.0.0.0/0 0.0.0.0/0
```
The value **0.0.0.0/0** on the source column refers to **all** trafic. So, in my case, I need to replace the first two entries of both the PREROUTING and OUTPUT chain:
**Note**: The default Docker subnet is **172.17.0.0/16**. If you changed the default configurations make sure to change them in the commands also.
**PREROUTING**
```
iptables -t nat -R PREROUTING 1 ! -s 172.17.0.0/16 -p tcp -m tcp --dport 80 -j REDIRECT --to-ports 8080
```
```
iptables -t nat -R PREROUTING 2 ! -s 172.17.0.0/16 -p tcp -m tcp --dport 443 -j REDIRECT --to-ports 8443
```
**OUTPUT**
```
iptables -t nat -R OUTPUT 1 ! -s 172.17.0.0/16 -d 127.0.0.1/32 -p tcp -m tcp --dport 443 -j REDIRECT --to-ports 8443
```
```
iptables -t nat -R OUTPUT 2 ! -s 172.17.0.0/16 -d 127.0.0.1/32 -p tcp -m tcp --dport 80 -j REDIRECT --to-ports 8080
```
Now, requests from the Docker container return with a 200 http status and everyone is happy 🤗 Hope this helps you if you are having a similar problem!
As a side note, while doing all this, I also needed to learn more about iptables and their different options. I found [this quick guide from **linode**](https://www.linode.com/docs/security/firewalls/control-network-traffic-with-iptables/) handy.
**Thanks for reading me!**