ManthanHD

Minimal Express server setup for API development

Posted on 28th April 2017 by Manthan Dave / 0 Comment

Initialise npm with defaults.

npm init

npm init

Create your main index.js entrypoint.

touch index.js

1	touch index.js

Install express, body-parser, morgan and winston packages.

npm install --save express body-parser morgan winston

1	npm install --save express body-parser morgan winston

Make your index.js look like this.

const express = require("express");
const app = express();

global.port = process.env.PORT || 3000;
global.logger = require("winston");
logger.level = process.env.LOG_LEVEL || "debug";

const bodyParser = require("body-parser");
app.use(bodyParser.json());

const morgan = require("morgan");
app.use(morgan('combined'));

app.get("/", function(req, res) {
    return res.send({message: "hello"});
});

app.listen(port, function(err) {
    if(err) {
        logger.error(`Failed to listen on port ${port}.`);
        return process.exit(1);
    }

    logger.info(`Listening on port ${port}.`);
});

const express = require("express");

const app = express();

global.port = process.env.PORT || 3000;

global.logger = require("winston");

logger.level = process.env.LOG_LEVEL || "debug";

const bodyParser = require("body-parser");

app.use(bodyParser.json());

const morgan = require("morgan");

app.use(morgan('combined'));

app.get("/", function(req, res) {

return res.send({message: "hello"});

});

app.listen(port, function(err) {

if(err) {

logger.error(`Failed to listen on port ${port}.`);

return process.exit(1);

}

logger.info(`Listening on port ${port}.`);

});

This is probably one of the most light weight node.js configuration that I have ever written for building simple REST web services.

In my opinion, this is a good starting point as it makes minimal assumptions about what you might need, letting you add whatever you need minimally on top.

Educational

Appending to crontab using a single shell command

Posted on 24th April 2017 by Manthan Dave / 0 Comment

Usually to edit crontab for a user, you login as that user and then run:

crontab -e

1	crontab -e

This usually opens up a text editor which then lets you edit the crontab. Once you are done, you save and quit, and this magically updates your crontab.

Today I was writing a script that needed to update crontab without any user interaction. After doing some digging, I found this neat way of updating my crontab;

(crontab -l ; echo "* 1 * * 1 /usr/bin/letsencrypt renew && service nginx restart")| crontab -

1	(crontab -l ; echo "* 1 * * 1 /usr/bin/letsencrypt renew && service nginx restart")\| crontab -

The above example is straight out of my shell script which renews my letsencrypt certificate and then restarts the nginx server.

Educational

Setting up an OAuth2 provider

Posted on 20th April 2017 by Manthan Dave / 0 Comment

In this post, we’re going to talk about installing and setting up your very own OAuth2 provider. If you have used Facebook or Twitter logins, you’d know that they have their own OAuth2 providers. In reality, those are more than just OAuth2 providers as they also have OpenID Connect on them, however, that will be a post for another day.

Why would I want an OAuth2 provider?

Well, there are many reasons why you’d want an OAuth2 provider.

Because its cool.
Because its hip.
Because, why not?

On a more serious note, if you have a bunch of applications running in your house, you can use your own OAuth2 provider to provide identity and custom authorisations to every app in a way that if one of those apps gets compromised, it won’t take your whole house down. This lets you operate all of your apps in a standard way.

Also, who in your family doesn’t want “Sign in via <insert_family_name>” button? 😛

For this post, we’re going to use Forgerock’s OpenAM version 13.

Continue reading →

Findings

Fixing docker service startup after using an alternative graph driver

Posted on 15th April 2017 by Manthan Dave / 0 Comment

So I was playing around with devicemapper docker storage driver the other day. It was quite nice but when I stopped the modified docker daemon and tried to start the docker service in “normal” way, I received the following error:

root@carbon:~# service docker start
Job for docker.service failed because the control process exited with error code. See "systemctl status docker.service" and "journalctl -xe" for details.

1 2	root@carbon:~# service docker start Job for docker.service failed because the control process exited with error code. See "systemctl status docker.service" and "journalctl -xe" for details.

Clearly something had gone wrong. Upon running:

systemctl status docker.service

1	systemctl status docker.service

I found the following line most helpful in fixing the error:

Jan 24 22:33:17 carbon dockerd[3753]: Error starting daemon: error initializing graphdriver: /var/lib/docker contains several valid graphdrivers: devicemapper, aufs; Please cleanup or explicitly choose storage driver (-s

1	Jan 24 22:33:17 carbon dockerd[3753]: Error starting daemon: error initializing graphdriver: /var/lib/docker contains several valid graphdrivers: devicemapper, aufs; Please cleanup or explicitly choose storage driver (-s

So I ran the following command in order to remove my devicemapper driver:

rm -rf /var/lib/docker/devicemapper

1	rm -rf /var/lib/docker/devicemapper

Boom it worked!

Alternatively, I could’ve backed it up to tmp instead by running:

mv /var/lib/docker/devicemapper /tmp/

1	mv /var/lib/docker/devicemapper /tmp/

But I didn’t need any of my images anyway so I removed it.

Hope this helps.

Findings

Which process is using this port?

Posted on 13th April 2017 by Manthan Dave / 0 Comment

Sometimes, I get errors like “address is already in use” but struggle to find out what’s using that port. This happens especially with loads of stuff running in background like docker, vagrant vms, local server instances, ssh tunnels etc.

Here’s an easy way to figure out whats running on a certain port:

netstat -vanp tcp | grep 8080

1	netstat -vanp tcp \| grep 8080

The second last column refers to the process using that port.

For example, running that on my mac:

➜ ~ netstat -vanp tcp | grep 8080
tcp4 0 0 *.8080 *.* LISTEN 65536 65536 5500 0

1 2	➜ ~ netstat -vanp tcp \| grep 8080 tcp4 0 0 .8080 .* LISTEN 65536 65536 5500 0

Indicates that process ID 5500 is using port 8080. Doing a process check on that tells me:

➜ ~ ps -ef | grep 5500
394661014 5500 5443 0 7:15am ?? 0:42.61 /Applications/VirtualBox.app/Contents/MacOS/VBoxHeadless --comment kitchen-awesomevm --startvm b459e3ea-566b-4184-a109-cf97338958aa --vrde config

1 2	➜ ~ ps -ef \| grep 5500 394661014 5500 5443 0 7:15am ?? 0:42.61 /Applications/VirtualBox.app/Contents/MacOS/VBoxHeadless --comment kitchen-awesomevm --startvm b459e3ea-566b-4184-a109-cf97338958aa --vrde config

Hope this helps!

ManthanHD

Minimal Express server setup for API development

Like this:

Appending to crontab using a single shell command

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Setting up an OAuth2 provider

Why would I want an OAuth2 provider?

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Fixing docker service startup after using an alternative graph driver

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Which process is using this port?

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Why would I want an OAuth2 provider?

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