Docker Multistage Builds for Hugo

In this tutorial I will demonstrate how to keep your docker container images nice and slim with the use of multistage builds for a Hugo documentation project.

Hugo is a static content generator so essentially that means that it will generate your markdown files into html. Therefore we don’t need to include all the content from our project repository as we only need the static content (html, css, javascript) to reside on our final container image.

What are we doing today

We will use the DOKS Modern Documentation theme for Hugo as our project example, where we will build and run our documentation website on a docker container, but more importantly make use of multistage builds to optimize the size of our container image.

Our Build Strategy

Since hugo is a static content generator, we will use a node container image as our base. We will then build and generate the content using `npm run build` which will generate the static content to `/src/public` in our build stage.

Since we then have static content, we can utilize a second stage using a nginx container image with the purpose of a web server to host our static content. We will copy the static content from our `build` stage into our second stage and place it under our defined path in our nginx config.

This way we only include the required content on our final container image.

Building our Container Image

First clone the docs github repository and change to the directory:

git clone https://github.com/h-enk/doks
cd doks

Now create a `Dockerfile` in the root path with the following content:

FROM node:16.15.1 as build
WORKDIR /src
ADD . .
RUN npm install
RUN npm run build
FROM nginx:alpine
LABEL demonstration.by Ruan Bekker <@ruanbekker>
COPY nginx/config/nginx.conf /etc/nginx/nginx.conf
COPY nginx/config/app.conf /etc/nginx/conf.d/app.conf
COPY — from=build /src/public /usr/share/nginx/app

As we can see we are copying two nginx config files to our final image, which we will need to create.

Create the nginx config directory:

mkdir -p nginx/config

The content for our main nginx config `nginx/config/nginx.conf`:

user nginx;
worker_processes auto;
error_log /var/log/nginx/error.log notice;
pid /var/run/nginx.pid;
events {
worker_connections 1024;
}
http {
include /etc/nginx/mime.types;
default_type application/octet-stream;
log_format main ‘$remote_addr — $remote_user [$time_local] “$request” ‘
‘$status $body_bytes_sent “$http_referer” ‘
‘“$http_user_agent” “$http_x_forwarded_for”’;
access_log /var/log/nginx/access.log main; sendfile on; # timeouts
client_body_timeout 12;
client_header_timeout 12;
keepalive_timeout 25;
send_timeout 10;
# buffer size
client_body_buffer_size 10K;
client_header_buffer_size 1k;
client_max_body_size 8m;
large_client_header_buffers 4 4k;

# gzip compression
gzip on;
gzip_vary on;
gzip_min_length 10240;
gzip_proxied expired no-cache no-store private auth;
gzip_types text/plain text/css text/xml text/javascript application/x-javascript application/xml;
gzip_disable “MSIE [1–6]\.”;
include /etc/nginx/conf.d/app.conf;
}

And in our main nginx config we are including a virtual host config `app.conf`, which we will create locally, and the content of `nginx/config/app.conf`:

server {
listen 80;
server_name localhost;
location / {
root /usr/share/nginx/app;
index index.html index.htm;
}
#error_page 404 /404.html;
# redirect server error pages to the static page /50x.html
error_page 500 502 503 504 /50x.html;
location = /50x.html {
root /usr/share/nginx/html;
}
}

Now that we have our docker config in place, we can build our container image:

docker build -t ruanbekker/hashnode-docs-blogpost:latest .

Then we can review the **size** of our container image, which is only `27.4MB` in size, pretty neat right.

docker images — filter reference=ruanbekker/hashnode-docs-blogpostREPOSITORY TAG IMAGE ID CREATED SIZE
ruanbekker/hashnode-docs-blogpost latest 5b60f30f40e6 21 minutes ago 27.4MB

Running our Container

Now that we’ve built our container image, we can run our documentation site, by specifying our host port on the left to map to our container port on the right in `80:80`:

docker run -it -p 80:80 ruanbekker/hashnode-docs-blogpost:latest

When you don’t have port 80 already listening prior to running the previous command, when you head to http://localhost (if you are running this locally), you should see our documentation site up and running:

Thank You

I have published this container image to ruanbekker/hashnode-docs-blogpost.

Thanks for reading, feel free to check out my website, feel free to subscribe to my newsletter or follow me at @ruanbekker on Twitter.

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Ruan Bekker

Ruan Bekker

DevOps Engineer and Open Source Enthusiast