diff --git a/sources/tech/20210104 Docker Compose- a nice way to set up a dev environment.md b/sources/tech/20210104 Docker Compose- a nice way to set up a dev environment.md new file mode 100644 index 0000000000..b2d719b02a --- /dev/null +++ b/sources/tech/20210104 Docker Compose- a nice way to set up a dev environment.md @@ -0,0 +1,249 @@ +[#]: collector: (lujun9972) +[#]: translator: ( ) +[#]: reviewer: ( ) +[#]: publisher: ( ) +[#]: url: ( ) +[#]: subject: (Docker Compose: a nice way to set up a dev environment) +[#]: via: (https://jvns.ca/blog/2021/01/04/docker-compose-is-nice/) +[#]: author: (Julia Evans https://jvns.ca/) + +Docker Compose: a nice way to set up a dev environment +====== + +Hello! Here is another post about [computer tools that I’ve appreciated][1]. This one is about Docker Compose! + +This post is mostly just about how delighted I was that it does what it’s supposed to do and it seems to work and to be pretty straightforward to use. I’m also only talking about using Docker Compose for a dev environment here, not using it in production. + +I’ve been thinking about this kind of personal dev environment setup more recently because I now do all my computing with a personal cloud budget of like $20/month instead of spending my time at work thinking about how to manage thousands of AWS servers. + +I’m very happy about this because previous to trying Docker Compose I spent two days getting frustrated with trying to set up a dev environment with other tools and Docker Compose was a lot easier and simpler. And then I told my sister about my docker-compose experiences and she was like “I KNOW, DOCKER COMPOSE IS GREAT RIGHT?!?!” So I thought I’d write a blog post about it, and here we are. + +### the problem: setting up a dev environment + +Right now I’m working on a Ruby on Rails service (the backend for a sort of computer debugging game). On my production server, I have: + + * a nginx proxy + * a Rails server + * a Go server (which proxies some SSH connections with [gotty][2]) + * a Postgres database + + + +Setting up the Rails server locally was pretty straightforward without resorting to containers (I just had to install Postgres and Ruby, fine, no big deal), but then I wanted send `/proxy/*` to the Go server and everything else to the Rails server, so I needed nginx too. And installing nginx on my laptop felt too messy to me. + +So enter `docker-compose`! + +### docker-compose lets you run a bunch of Docker containers + +Docker Compose basically lets you run a bunch of Docker containers that can communicate with each other. + +You configure all your containers in one file called `docker-compose.yml`. I’ve pasted my entire `docker-compose.yml` file here for my server because I found it to be really short and straightforward. + +``` +version: "3.3" +services: + db: + image: postgres + volumes: + - ./tmp/db:/var/lib/postgresql/data + environment: + POSTGRES_PASSWORD: password # yes I set the password to 'password' + go_server: + # todo: use a smaller image at some point, we don't need all of ubuntu to run a static go binary + image: ubuntu + command: /app/go_proxy/server + volumes: + - .:/app + rails_server: + build: docker/rails + command: bash -c "rm -f tmp/pids/server.pid && source secrets.sh && bundle exec rails s -p 3000 -b '0.0.0.0'" + volumes: + - .:/app + web: + build: docker/nginx + ports: + - "8777:80" # this exposes port 8777 on my laptop +``` + +There are two kinds of containers here: for some of them I’m just using an existing image (`image: postgres` and `image: ubuntu`) without modifying it at all. And for some I needed to build a custom container image – `build: docker/rails` says to use `docker/rails/Dockerfile` to build a custom container. + +I needed to give my Rails server access to some API keys and things, so `source secrets.sh` puts a bunch of secrets in environment variables. Maybe there’s a better way to manage secrets but it’s just me so this seemed fine. + +### how to start everything: `docker-compose build` then `docker-compose up` + +I’ve been starting my containers just by running `docker-compose build` to build the containers, then `docker-compose up` to run everything. + +You can set `depends_on` in the yaml file to get a little more control over when things start in, but for my set of services the start order doesn’t matter, so I haven’t. + +### the networking is easy to use + +It’s important here that the containers be able to connect to each other. Docker Compose makes that super simple! If I have a Rails server running in my `rails_server` container on port 3000, then I can access that with `http://rails_server:3000`. So simple! + +Here’s a snippet from my nginx configuration file with how I’m using that in practice (I removed a bunch of `proxy_set_header` lines to make it more clear) + +``` +location ~ /proxy.* { + proxy_pass http://go_server:8080; +} +location @app { + proxy_pass http://rails_server:3000; +} +``` + +Or here’s a snippet from my Rails project’s database configuration, where I use the name of the database container (`db`): + +``` +development: + <<: *default + database: myproject_development + host: db # <-------- this "magically" resolves to the database container's IP address + username: postgres + password: password +``` + +I got a bit curious about how `rails_server` was actually getting resolved to an IP address. It seems like Docker is running a DNS server somewhere on my computer to resolve these names. Here are some DNS queries where we can see that each container has its own IP address: + +``` +$ dig +short @127.0.0.11 rails_server +172.18.0.2 +$ dig +short @127.0.0.11 db +172.18.0.3 +$ dig +short @127.0.0.11 web +172.18.0.4 +$ dig +short @127.0.0.11 go_server +172.18.0.5 +``` + +### who’s running this DNS server? + +I dug into how this DNS server is set up a very tiny bit. + +I ran all these commands outside the container, because I didn’t have a lot of networking tools installed in the container. + +**step 1**: find the PID of my Rails server with `ps aux | grep puma` + +It’s 1837916. Cool. + +**step 2**: find a UDP server running in the same network namespace as PID `1837916` + +I did this by using `nsenter` to run `netstat` in the same network namespace as the `puma` process. (technically I guess you could run `netstat -tupn` to just show UDP servers, but my fingers only know how to type `netstat -tulpn` at this point) + +``` +$ sudo nsenter -n -t 1837916 netstat -tulpn +Active Internet connections (only servers) +Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name +tcp 0 0 127.0.0.11:32847 0.0.0.0:* LISTEN 1333/dockerd +tcp 0 0 0.0.0.0:3000 0.0.0.0:* LISTEN 1837916/puma 4.3.7 +udp 0 0 127.0.0.11:59426 0.0.0.0:* 1333/dockerd +``` + +So there’s a UDP server running on port `59426`, run by `dockerd`! Maybe that’s the DNS server? + +**step 3**: check that it’s a DNS server + +We can use `dig` to make a DNS query to it: + +``` +$ sudo nsenter -n -t 1837916 dig +short @127.0.0.11 59426 rails_server +172.18.0.2 +``` + +But – when we ran `dig` earlier, we weren’t making a DNS query to port 59426, we were querying port 53! What’s going on? + +**step 4**: iptables + +My first guess for “this server seems to be running on port X but I’m accessing it on port Y, what’s going on?” was “iptables”. + +So I ran iptables-save in the container’s network namespace, and there we go: + +``` +$ sudo nsenter -n -t 1837916 iptables-save +.... redacted a bunch of output .... +-A DOCKER_POSTROUTING -s 127.0.0.11/32 -p udp -m udp --sport 59426 -j SNAT --to-source :53 +COMMIT +``` + +There’s an iptables rule that sends traffic on port 53 to 59426. Fun! + +### it stores the database files in a temp directory + +One nice thing about this is: instead of managing a Postgres installation on my laptop, I can just mount the Postgres container’s data directory at `./tmp/db`. + +I like this because I really do not want to administer a Postgres installation on my laptop (I don’t really know how to configure Postgres), and conceptually I like having my dev database literally be in the same directory as the rest of my code. + +### I can access the Rails console with `docker-compose exec rails_server rails console` + +Managing Ruby versions is always a little tricky and even when I have it working, I always kind of worry I’m going to screw up my Ruby installation and have to spend like ten years fixing it. + +With this setup, if I need access to the Rails console (a REPL with all my Rails code loaded), I can just run: + +``` +$ docker-compose exec rails_server rails console +Running via Spring preloader in process 597 +Loading development environment (Rails 6.0.3.4) +irb(main):001:0> +``` + +Nice! + +### small problem: no history in my Rails console + +I ran into a problem though: I didn’t have any history in my Rails console anymore, because I was restarting the container all the time. + +I figured out a pretty simple solution to this though: I added a `/root/.irbrc` to my container that changed the IRB history file’s location to be something that would persist between container restarts. It’s just one line: + +``` +IRB.conf[:HISTORY_FILE] = "/app/tmp/irb_history" +``` + +### I still don’t know how well it works in production + +Right now my production setup for this project is still “I made a digitalocean droplet and edited a lot of files by hand”. + +I think I’ll try to use docker-compose to run this thing in production. My guess is that it should work fine because this service is probably going to have at most like 2 users at a time and I can easily afford to have 60 seconds of downtime during a deploy if I want, but usually something goes wrong that I haven’t thought of. + +A few notes from folks on Twitter about docker-compose in production: + + * `docker-compose up` will only restart the containers that need restarting, which makes restarts faster + * there’s a small bash script [wait-for-it][3] that you can use to make a container wait for another service to be available + * You can have 2 docker-compose.yaml files: `docker-compose.yaml` for DEV, and `docker-compose-prod.yaml` for prod. I think I’ll use this to expose different nginx ports: 8999 in dev and 80 in prod. + * folks seemed to agree that docker-compose is fine in production if you have a small website running on 1 computer + * one person suggested that Docker Swarm might be better for a slightly more complicated production setup, but I haven’t tried that (or of course Kubernetes, but the whole point of Docker Compose is that it’s super simple and Kubernetes is certainly not simple :) ) + + + +Docker also seems to have a feature to [automatically deploy your docker-compose setup to ECS][4], which sounds cool in theory but I haven’t tried it. + +### when doesn’t docker-compose work well? + +I’ve heard that docker-compose doesn’t work well: + + * when you have a very large number of microservices (a simple setup is best) + * when you’re trying to include data from a very large database (like putting hundreds of gigabytes of data on everyone’s laptop) + * on Mac computers, I’ve heard that Docker can be a lot slower than on Linux (presumably because of the extra VM). I don’t have a Mac so I haven’t run into this. + + + +### that’s all! + +I spent an entire day before this trying to configure a dev environment by using Puppet to provision a Vagrant virtual machine only to realize that VMs are kind of slow to start and that I don’t really like writing Puppet configuration (I know, huge surprise :)). + +So it was nice to try Docker Compose and find that it was straightforward to get to work! + +-------------------------------------------------------------------------------- + +via: https://jvns.ca/blog/2021/01/04/docker-compose-is-nice/ + +作者：[Julia Evans][a] +选题：[lujun9972][b] +译者：[译者ID](https://github.com/译者ID) +校对：[校对者ID](https://github.com/校对者ID) + +本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出 + +[a]: https://jvns.ca/ +[b]: https://github.com/lujun9972 +[1]: https://jvns.ca/#cool-computer-tools---features---ideas +[2]: https://github.com/yudai/gotty/ +[3]: https://github.com/vishnubob/wait-for-it +[4]: https://docs.docker.com/cloud/ecs-integration/