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Learn Docker - from the beginning, part III databases and linking

Chris Noring on February 15, 2019

Follow me on Twitter, happy to take your suggestions on topics or improvements /Chris TLDR; this is somewhat of a long read but there is mic drop...

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Khaja Moinuddin Mohammed • Jul 24 '19

Hi @chris can you add this line before "Let’s try to run our node app.js command again and this time we get this: node app.js",

create table with the name Customer before running node app.js with below command

CREATE DATABASE Customers;

without creating the db, i was getting error, but after creating the db it resolved.

I ain't sure if this is how it needs to be done, as am no expert with sql dbs. Please correct me if am wrong.

Anjum Rashid • Sep 10 '22

Fell into the same trap as well. Thanks for pointing it out.

Dragane • Dec 5 '19 • Edited

That is correct. We created the Customers database on the host mysql server but we left the container database untouched. Manual creation of the Customers database is required on the container.

Anjum Rashid • Sep 10 '22 • Edited

If you're doing this module on Windows host with Git Bash, mysql server can be set up manually the following way:

Download & extract the MySQL Community Server zip archive on a persistant storage
Add path-to-mysql-directory/bin to PATH variable
Create a data directory under mysql directory
Start the server for the first time with mysqld --initialize --console

Now you're good to follow along the rest!

Jordan Walker • Apr 21 '19

Hey, nice work!

Just one thing, I'm stuck on where we setup the network. I've created my network with

docker network create --driver bridge isolated

and then ran my containers with

docker run -d -p 8000:3000 --net isolated --name jayy jayywalker/node

docker run -p 8001:3306 --net isolated --name db -e MYSQL_ROOT_PASSWORD=dddd -d mysql

Of course since I've ran the app container before the mysql it won't find it, but even after restarting the app container I receive the following error:

/app/app.js:13
    throw err
    ^

Error: connect ETIMEDOUT
    at Connection._handleConnectTimeout (/app/node_modules/mysql/lib/Connection.js:412:13)
    at Object.onceWrapper (events.js:281:20)
    at Socket.emit (events.js:193:13)
    at Socket._onTimeout (net.js:450:8)
    at listOnTimeout (internal/timers.js:535:17)
    at processTimers (internal/timers.js:479:7)
    --------------------
    at Protocol._enqueue (/app/node_modules/mysql/lib/protocol/Protocol.js:144:48)
    at Protocol.handshake (/app/node_modules/mysql/lib/protocol/Protocol.js:51:23)
    at Connection.connect (/app/node_modules/mysql/lib/Connection.js:119:18)
    at Object.<anonymous> (/app/app.js:11:5)
    at Module._compile (internal/modules/cjs/loader.js:816:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:827:10)
    at Module.load (internal/modules/cjs/loader.js:685:32)
    at Function.Module._load (internal/modules/cjs/loader.js:620:12)
    at Function.Module.runMain (internal/modules/cjs/loader.js:877:12)
    at internal/main/run_main_module.js:21:11

It worked fine using link.

Michele delle Noci • Sep 10 '19

What string are you using as host in the node app? I've noticed that when you use networks instead of links you have to reference to other containers inside the networks by their names.

Johan Lindstrom • Feb 12 '20

This needs mentioning in the article, at the end of the "Expand our knowledge on linking — there is another way" section.

Chris Noring • Feb 14 '20

thanks for the feedback Johan.. Haven't had time to update... But yes will look into improving this section

Chris Noring • Apr 21 '19 • Edited

hi Jordan. Thanks for your comment. Let me get back to you in a couple of days

Chris Noring • Sep 11 '19

you should be using the name of the mysql container as host property

Mayank Gupta • Feb 12 '20

I am getting the same error even after I have set the host property as "mysql". Could you please point where I am going wrong?

Chris Noring • Feb 12 '20

Thanks for reaching out Mayank. Let m get back to you shortly

aRtoo • Nov 6 '19

docker run -d -p 8000:3000 --net isolated_network --name my-container chrisnoring-node

docker run -p 8000:3306 --net isolated_network --name mysql-db -e MYSQL_ROOT_PASSWORD=complexpassword -d mysql

both have the same exposed port. this isn't allowed right? or am i doing it wrong? i have an error

Bind for 0.0.0.0:8000 failed: port is already allocated.

Chris Noring • Nov 6 '19

hi. Yes, you are correct. Should 8001 for the database, or at least not 8000. Thanks for noticing :)

AymDev • Apr 24 '19

There are things I did not get when we used --net. How do the containers communicate ?

Mine could not find the MySQL container with the previous "mysql" alias. After running docker inspect mysql-db I used the IP stated from the output at NetworkSettings.Networks.isolated_network.Gateway as the mysql host parameter.
I doubt that this is a reliable solution, how should I proceed to make it easier ?

Scott Seager • Mar 17 '19

Great article (and series), Chris!

I’ve got a quick question about persistence with the MySQL container. I might have missed it somewhere, but was wondering where the actual MySQL data winds up so that it isn’t lost when the container is restarted later.

Ie. On a native Linux installation these would wind up in /var/lib/mysql on the host machine. Where does the dockerized MySQL container put them? Does it implicitly mount a host file system volume in the same location?

Serhiy Neskhodovskiy • May 6 '19 • Edited

You actually bring up an important issue Scott. The whole point about containers is that they are disposable. A good architecture assumes that any container may be destroyed and re-created (from a Dockerfile) at any later moment. But if we destroy the MySQL container we will eventually lose the database. Not a big deal for development, but sounds scary in production, right? One particular consequence, we have to stick to mysql image once downloaded and we won't be able to update to a newer image or to make changes to the image, without destroying the container and losing all data.

The solution? Separate data (mysql database) from the application (mysql container). That's what volumes are for - theoretically. The first idea coming to mind, let's put /var/lib/mysql (or whatever directory MySQL uses as storage) into a volume and mount it into the container, right? Not sure about you, but I had a bunch of low-level issues trying to port this directory from a Windows to a Linux host. The problem turned out to be the difference in how MySQL reads and writes to disk on different platforms.

I don't have a viable solution for this yet, and I'll be happy to hear one.

Vitaliy Rudnytskiy • Mar 22 '19

Hi Scott. Great question! I've been asking it myself as well :)

I am using Docker Desktop on Mac, so in my case Docker is using a disk image named Docker.raw located in ~/Library/Containers/com.docker.docker/Data/vms/0. And this is where it stores all containers and images. So, you won't see exact the same structure of folders and files on a host as you see in the container.

Regards,
-Vitaliy

mhussajn • Mar 18 '19

Great content!

Small nitpick - after creating a network, you won't be able to run database container with the command in the article, because port 8000 will already be allocated by first container :)