Modern Python Projects Transcripts
Chapter: Deployment
Lecture: Auto reboot and auto update
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0:00
One of the problems that we have with our Docker application right now is that if we rebooted the droplet or if this container stops,
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for some reason, it won't automatically restart our docker container. So let me show you what I mean.
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Let's start docker container in a detached mode, so I still can see my terminal. We can see that our container is running, and if we go to the browser,
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it's here. So, if I reboot this machine right now, Docker won't be able to restart our container, So let's give it a few seconds.
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If we check for running docker containers, we will see that there are no containers and our website is down.
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It keeps loading and then it's going to crash. So this problem can actually be easily solved with providing one additional parameter.
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If we run Docker with the restart parameter and we tell it to restart, unless we explicitly stop this container,
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Docker will automatically restart this container whenever we reboot this Droplet or whenever something goes wrong
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and container goes down. So let's do another test. Let's go to the browser, it's working and let's reboot the machine.
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And if we list the running containers again. You can see that after the reboot, Docker has restarted our container. Cool.
1:58
So with the simple trick, we told Docker to automatically reboot our container if something
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goes wrong. Another thing that we could do is to have some kind of very simple continues delivery mechanism. For example,
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whenever we push a new version of image to Docker Hub, we want to automatically deploy. And this we can do with the watchtower tool.
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So watch tower is basically a container that will monitor other containers, and if there is a new version of image available,
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it will restart them. All we have to do is to take this piece of code and run it inside our droplet. I will, however, make some modifications.
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So first I want to also run in this restart mode. So whenever our droplet goes down, we will also restart the watchtower.
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And I also want to change the default interval in which Watchtower will be pulling for
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new images by default. Watchtower will check every five minutes if there is a new version of an image under Docker Hub,
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which is a good default because right now Docker has some limitations of how many images
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you can pull per hour. But I don't want you to sit here and wait for five minutes to see if our image was updated.
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So, I'm going to change the pull interval to 15 seconds. Okay, so we have the watchtower running. Let's just restart our uptime our website.
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So, let's see if our uptimer is running right now. And as you can see it is, So now we have to go back to our initial code,
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change something and rebuild retag and republish new docker image. So, let's change this online to lower case again.
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And that's it. That's not like that. I was experimenting with something in the background. Let's retag and push. Okay,
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Now we go back to our server and we have to wait for a bit We can use the Docker PS command to see.
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When was the last time one of the containers was restarted. And as you can see, our uptimer website was restarted less than a second
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ago. So yeah, that was the watchtower would detected that there is a new image. It pulled this image and it restarted our container,
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right. So now if we go back to the browser and if we refresh, we should see the new version. Cool. Yeah, so it's working.
5:34
So, that's how you can have a very simple continues delivery mechanism with Watchtower pulling new images. It's far from perfect,
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because when watchtower is updating your container, it's actually stopping it. So if you have a visitor coming to your website during
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the time when the new images being deployed well, your website will be down. But to properly deal with this problem,
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you would need to have two different servers and the load balancer. And when you're updating one of those servers,
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the load balancer will stop sending traffic there. And then you will update the other server Stop load balancer from sending traffic there and
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then you should be fine, which sounds like a lot of work, and it has a lot of work. You can do this with kubernetes, but for our very simple website,
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using the watchtower is perfectly fine. Yeah, that's how you can build and deploy docker images.
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In the next lesson, I will talk about building something more advanced that requires,for example having a database or some kind of other external server.