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WTF is a container?

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Re: WTF is a container?

#201

Post by novaleaf »

> The way virtual machines work, however, is by packaging the operating system and code together. The operating systems on the virtual machines believes that it has a server to its own, but in reality, it’s sharing the server with a bunch of other virtual machines — all of which run their own operating systems and don’t know of each other. Underneath it all is the host operating system that makes all of these guests believe they are the most important thing in the world. You can see why this is a problem. The guest virtual machines basically run on emulated servers, and that creates a lot of overhead and slows things down (but in return, you could run lots of different operating systems on the same server, too).

Wait a second. Isn't this the whole point of hardware virtualization support? So that hypervisors don't have all those VM overhead slowing things down?

Re: WTF is a container?

#202

Post by elsonrodriguez »

paulddraper wrote: post #129
vidarh wrote: post #69

Earlier quoted context omitted.

> How is a container different from just installing all the dependencies along with an application? Once the image is built, you can get another installation that is guaranteed to be identical. You can do that with VM images too, but you can not reasonably do that if you try to install multiple applications side by side in a single VM without further isolation - there are too many ways they can interact. > Isolation…

> Try to get an application - statically compiled or not - to run across different Linux distributions, and you will see why this matters. Done. A statically compiled application has no other dependencies.

This is the eventual future.

What most people don't realize is that a large part of Docker's value is in being a generic static compiler for languages that don't have that feature.

Pretty soon you can expect raw process support in many "container" management systems, where you just provide it a linux binary which are then run in isolated cgroups and namespaces.

Re: WTF is a container?

#203

Post by shoover »

pjmlp wrote: post #195
shoover wrote: post #178

Earlier quoted context omitted.

I'm missing the initial assumption. What is the connection between Docker and traction for Go and OCaml? People are using the latter in order to simply avoid containers?

Parts of Docker are implemented on them. So anyone that wants to improve Docker or adapt it to their distribution of choice needs to eventually use them. For example, Microsoft did several contributions in Go for making Docker run on Windows. The TCP/IP stack used by Docker on OS X is taken from MirageOS, written in OCaml.

Got it. Thanks.

Re: WTF is a container?

#204

Post by moondev »

Azeralthefallen wrote: post #101

I remember going to AWS Reinvent last year and having some beers with a bunch of people who did devops. We started talking about tools, and they were utterly flabbergasted, that we had not embraced docker. They went on an on about how simple docker made HA, and handling fail overs/maintenance. More or less made it seem like it was the greatest thing since sliced bread. Me and a few coworkers decided to try and docker…

The problem is you are trying to run a production environment with a development tool. Manually doing "docker run" is not how you deploy containers. Kubernetes is designed to run containers and addresses the most common issues.

> Making containers work together, for example we use a logging agent, we decided to make that its own container. Then actually getting a way to share a log directory with the agent, was very painful and unclear. (Honestly the single most frustrating thing i recall was asking for advice in irc and more or less being told i am doing it wrong)

kubernetes handles shared directories easily with all containers in a pod. If you need to share across pods you can use persistentVolumeRequests

> Containers would randomly crash under load exiting with error 137 out of memory. Apparently a few of our services would randomly leak memory, but only when running inside a docker container vs ubuntu 14.04. (I never figured this out)

Kubernetes provides replication controllers that will always re-launch or provision the number of desired pods for a service. It also provides health checks just like an aws elb to determine if a pod is healthy. You can also set resource limits (cpu and memory) per pod.

> Random hanging issues, suddenly docker exec is hanging. Being told to revert to an older version, or install a newer version is tiring and makes my environment very inconsistent.

Docker exec should not really be used on a running service in production, all of your provisioning should happen in the dockerfile to build the image

> Trying to debug why our app in the container isn't working is not fun at all.

If your application is 10-factor, you can easily tail the logs of any container at anytime

Re: WTF is a container?

#205

Post by zeveb »

jjnoakes wrote: post #145
ChoHag wrote: post #58

Earlier quoted context omitted.

The concept is great but it's also not original. It's called "processes". Docker is little more than a mass of complication laid atop fork+exec. That's why nobody can get it right - because we already did.

How is "your own network, your own view of the file system, your own view of the process table, your own view of the user IDs, ..." the same as "processes"?

Plan 9 is knocking on the door and would like to have a word …

Re: WTF is a container?

#206

Post by chewchew »

tigershark wrote: post #130
chewchew wrote: post #27

Earlier quoted context omitted.

Docker gives you the building blocks, but that means you have more pieces to arrange and manage. Take a look at Docker Compose if you haven't already, since the Docker CLI only gets you so far when you're creating apps that consist of multiple containers. I think the best approach for your cert issue is to abstract that into a separate service (nginx is an option, but I'd recommend the Rancher approach below). Yes, t…

Seriously? If something crashes continuously in production then the solution is "just pass the --restart=always flag. I really wonder if you guys are really using docker in prod. I would never use something like that to manage important transactions.

As someone said, this is the normal behavior in the Erlang/Elixir world, and it seems to have worked extremely well for the telecom industry.

That said, my reply was to someone running an IRC server, presumably on a single server, so don't stretch my advice to a production app handling millions of transactions. Obviously the core issue is that the app crashes, and it's still up to him to fix that. This is almost certainly a problem with his app/config, not Docker itself (though it ain't perfect). If it's something that happens every 6 months, then auto restarting will probably save him a lot of problems. If your transactions are so precious, don't pass the flag- it's up to you.

Re: WTF is a container?

#207

Post by chewchew »

holografix wrote: post #42
chewchew wrote: post #27

Earlier quoted context omitted.

Docker gives you the building blocks, but that means you have more pieces to arrange and manage. Take a look at Docker Compose if you haven't already, since the Docker CLI only gets you so far when you're creating apps that consist of multiple containers. I think the best approach for your cert issue is to abstract that into a separate service (nginx is an option, but I'd recommend the Rancher approach below). Yes, t…

Hey chewchew you seem to be knowledgeable on docker-compose. What's the easiest way to get a .yml on a cloud server somewhere and let it assemble it assemble the containers for you? Also, do you know where containers set environment variables? The official Postgres makes available something like PG_PORT_3542 and u can just refer to it from another container. Where I can't seem to do the same with the Redis one...

The absolute easiest is probably Docker Cloud. I've checked it out but haven't really used it much. It's still relatively immature but if you just want to deploy and forget something simple, this is probably the way to go.

If you want to use your own Linux host, then the simplest way would probably just be to SSH into the box, git pull, and run "docker-compose build && docker-compose up".

Setting environment variables is pretty easy, but I don't think you need them in this case. If you're trying to make a redis or postgres container available to another container (your app), then you can do so easily with links in docker-compose. Something like:

    myapp:
        image: myimage:0.0.1
        command: cmd to run
        links:
        - redis:redis
        ports:
        - 80:8000
        environment:
        - hardcoded_var=my_env_value
        - var_from_host=${host_var}
    redis:
        image: redis:latest
You can then access redis from the myapp service using the hostname "redis" and the default port "6379". So, "telnet redis 6379" would work from the myapp container (assuming telnet is actually installed). The redis port isn't even publicly exposed- it's only available to myapp.

If you need to define environment variables, you can do so with an environment dict as shown above. There are a few other ways to define env vars:

https://docs.docker.com/compose/compose-file/#variable-subst...

https://docs.docker.com/compose/environment-variables/#/the-...

Re: WTF is a container?

#208

Post by bboreham »

sigjuice wrote: post #193
bboreham wrote: post #132

Earlier quoted context omitted.

Takes about 2 seconds to fix: $ docker run -ti alpine /bin/sh / # apk add --update curl fetch http://dl-cdn.alpinelinux.org/alpine/v3.4/main/x86_64/APKINDEX.tar.gz fetch http://dl-cdn.alpinelinux.org/alpine/v3.4/community/x86_64/APKINDEX.tar.gz (1/4) Installing ca-certificates (20160104-r4) (2/4) Installing libssh2 (1.7.0-r0) (3/4) Installing libcurl (7.50.3-r0) (4/4) Installing curl (7.50.3-r0) Executing busybox-1.2…

Hitting dl-cdn.alpinelinux.org repeatedly for simple things is probably not nice. Is there an easy way to have a local alpine mirror?

I'm not suggesting this would be done repeatedly. Just when you need to debug something.

Nonetheless: https://wiki.alpinelinux.org/wiki/How_to_setup_a_Alpine_Linu...

Re: WTF is a container?

#209

Post by chewchew »

X86BSD wrote: post #137
tigershark wrote: post #130

Earlier quoted context omitted.

Seriously? If something crashes continuously in production then the solution is "just pass the --restart=always flag. I really wonder if you guys are really using docker in prod. I would never use something like that to manage important transactions.

No the correct solution is to debug the issue not just reboot/restart/reinit the damn thing. This mentality is WHY Linux/docker/containers/Linux worlds NIH syndrome, is such a tire fire.

It's not one or the other. Restarting might save you some downtime if you're running a single IRC container. That doesn't mean you shouldn't find and resolve the root issue. Normally I just rollback to the previous version container if I have a recurring issue.

Windows containers are now available, if you can't stand linux: https://msdn.microsoft.com/en-us/virtualization/windowsconta...

Anyway, don't use containers if you don't want to. I'm glad I invested the time since I understand them very well and use them to my advantage. But I did have to learn a lot and experiment with a bunch of tools, and maybe that's not worth it to you.

Re: WTF is a container?

#210

Post by lowbloodsugar »

dancek wrote: post #5

I agree that containers (both for shipping and servers) are a great idea. And because I'm tired of always configuring servers, I decided to give it a try some time ago. I wrapped my IRC client (weechat + glowing-bear) in a Docker container. Oh, not a container though, because I also needed https, which meant I needed either a mechanism to build and update letsencrypt certs in the weird format that weechat expects, or…

Someone told me that I should switch to using shipping containers instead of my current method.

Unfortunately, when my cattle arrived in the US, they were all dead. I was told containers "would just work".

After some experimentation, we managed to get our cattle in a container by building a system that correctly managed food and waste. Then we found a partner who had successfully packaged sheep and so we just used that. Unfortunately, they appeared to have a leak in their waste management system, and the container overflowed and all the sheep died. We did not have this problem when the sheep were able to fill the entire hold with their output.

Clearly the idea that shipping containers just work is a gross oversimplification. In fact containers seem to be complex thingamabobs with multiple points of failure.

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