Category: nginx

The future is here! In my previous article, Testing Out the Digital Ocean Container Registry, I talked about using the Digital Ocean Container Registry to build a custom nginx. In that article, I talked about the future, aka a future, aka this post. When I moved to WordPress, I did so using Digital Ocean’s 1-Click install to drop WordPress into my Kubernetes cluster. This was the easy way to go for sure. I already run Kubernetes so deploying it to an existing cluster made life easier on me. Who doesn’t love it when life is made easier?

There are a few drawbacks to the 1-Click install. I’m planning to tinker with something really cool down the road to fix one of those problems (I know the future again). Luckily, I’m going to address my first initial concern in this post. What is that concern you ask? Protecting my WordPress admin of course! Sure, there are a number of WordPress vulnerabilities roaming around and talks of zero days and the sort. I make life easier on any attacker if I just leave my WordPress admin open to anyone. In this post, we look at taking my custom nginx and deploying it in front of my WordPress site to enforce IP access control to the admin page.

Setting Up the Container Registry for Kubernetes

In my Testing Out the Digital Ocean Container Registry, I explained how to get a custom nginx into the Container Registry. In order to use that container and registry with my cluster, I had to enable DigitalOcean Kubernetes integration in the settings of the registry. You can do the same by doing the following:

1. Login to your DigitalOcean account
2. Go to the Container Registry link
3. Click on the Settings tab of the Container Registry
4. Click the Edit button next to DigitalOcean Kubernetes Integration
5. Place a check mark next to the Kubernetes clusters that you want to have access to this registry (Note, if you have multiple namespaces, this action will add access for all namespaces).

Once these steps are complete, you can confirm access by looking for a new secrets in your cluster:

# kubectl get secrets
NAME                   TYPE                                  DATA   AGE
default-token          kubernetes.io/service-account-token   3      423d
json-key               kubernetes.io/dockerconfigjson        1      396d
k8-registry            kubernetes.io/dockerconfigjson        1      18d
key-secret             Opaque                                2      419d

Notice the k8-registry secret that I now have in my secrets list? You can also see that this exists in my wordpress namespace as well:

# kubectl get secrets -n wordpress
NAME                  TYPE                                  DATA   AGE
default-token         kubernetes.io/service-account-token   3      18d
k8-registry           kubernetes.io/dockerconfigjson        1      18d
wp                    Opaque                                1      18d
wp-db                 Opaque                                2      18d

Adding Nginx to the Cluster

This should be super easy! I start by first creating configMap that stores my Nginx configuration:

apiVersion: v1
kind: ConfigMap
metadata:
  name: nginx-config
  namespace: wordpress
  labels:
    app: nginx
    release: wordpress
data:
  siteConfig: |
    server {
        listen 8080 default_server;
        listen [::]:8080 default_server;

        root /var/www/html;

        index index.html index.htm index.nginx-debian.html;

        server_name _;

        location /status {
                return 200 "healthy\n";
        }

        location / {
                proxy_pass http://wordpress;
                proxy_set_header Host blog.shellnetsecurity.com;
                proxy_set_header X-Forwarded-For $remote_addr;
        }

        location /admin {
                allow 1.1.1.1;
                allow 2.2.2.2;
                deny all;
                proxy_pass http://wordpress;
                proxy_set_header Host blog.shellnetsecurity.com;
                proxy_set_header X-Forwarded-For $remote_addr;
        }

        location /wp-admin {
                allow 1.1.1.1;
                allow 2.2.2.2;
                deny all;
                proxy_pass http://wordpress;
                proxy_set_header Host blog.shellnetsecurity.com;
                proxy_set_header X-Forwarded-For $remote_addr;
        }
    }

  serverConfig: |
    user www-data;
    worker_processes auto;
    pid /run/nginx.pid;
    include /etc/nginx/modules-enabled/*.conf;

    events {
        worker_connections 768;
    }

    http {
        sendfile on;
        tcp_nopush on;
        tcp_nodelay on;
        keepalive_timeout 65;
        types_hash_max_size 2048;
        include /usr/local/nginx/conf/mime.types;
        default_type application/octet-stream;
        access_log /dev/stdout;
        error_log /dev/stdout;
        gzip on;
        
        include /etc/nginx/sites-enabled/*;
    }

    daemon off;

I mostly added a set of standard nginx configurations. If you look at the serverConfig closely, you’ll notice that I’ve directed the access_log and error_log to /dev/stdout. This is so all of the logs are written to stdout (duh). This also allows me to run kubectl logs -f on the created pod and see the access and error logs.

Nginx is going to be acting like a reverse proxy so I took a relatively standard default site-available configuration and added a few new location blocks. The /status block is simply for me to perform healthchecks on the running nginx instance. The other statements are proxy_pass statements to send requests to the “wordpress” pod that was installed by the 1-Click install. I’m also making sure that I send over the Host header with blog.shellnetsecurity.com. If I don’t do this, the 1-Click install will build funky URLs that don’t work. Luckily, it will read the Host header and build links based upon that. I force the host header to be what I want with this statement.

Finally, you’ll see my allow statements for 1.1.1.1 and 2.2.2.2 (not really my IPs but let’s play make believe). These are followed by deny all. This should make it so that only my 1.1.1.1 and 2.2.2.2 addresses are allowed to /admin and /wp-admin. All others will be denied.

Next, I create a Deployment yaml that tells Kubernetes what containers to build and how to use my configMap:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx
  namespace: wordpress
  labels:
    app: nginx
    release: wordpress
spec:
  replicas: 2
  selector:
    matchLabels:
      app: nginx
      release: wordpress
  strategy:
    rollingUpdate:
      maxSurge: 25%
      maxUnavailable: 25%
    type: RollingUpdate
  template:
    metadata:
      labels:
        app: nginx
        release: wordpress
    spec:
      volumes:
      - name: siteconfig
        configMap:
          name: nginx-config
          items:
          - key: siteConfig
            path: default
      - name: serverconfig
        configMap:
          name: nginx-config
          items:
          - key: serverConfig
            path: nginx.conf
      imagePullSecrets:
      - name: k8-registry
      containers:
      - name: nginx
        image: registry.digitalocean.com/k8-registry/c-core-nginx:1.1
        ports:
        - containerPort: 8080
        volumeMounts:
        - name: siteconfig
          mountPath: /etc/nginx/sites-enabled/default
          subPath: default
        - name: serverconfig
          mountPath: /usr/local/nginx/conf/nginx.conf
          subPath: nginx.conf

Take note to the blue colored text above. I am using the imagePullSecrets configuration to tell kubernetes that it will need credentials to access the container registry where my image sits. I am also pointing it to the k8-registry credentials that were added by the DigitalOcean Kubernetes Integration change we made earlier. Finally, I am also providing the full path, version tag included, to the custom image I am hosting in the DigitalOcean registry with the image statement pointing to registry.digitalocean.com/k8-registry/c-core-nginx:1.1.

Next up, I need to add a NodePort that I can configure on the load balancer to send traffic over.

apiVersion: v1
kind: Service
metadata:
  namespace: wordpress
  name: nginx
  labels:
    app: nginx
    release: wordpress
spec:
  selector:
    app: nginx
    release: wordpress
  type: NodePort
  ports:
    - port: 8080
      nodePort: 31645

So I do a little kubectl apply -f to those yaml files I just created. Everything comes up. Next step is to setup the load balancer to forward traffic over. Since I have the nodePort configured as 31645, I just need to tell the load balancer to send traffic that I want to that port. I don’t want to mess with the existing setup so I decide to simply forward http port 8443 over to http port 31645.

Everything should be all set, so let’s open a browser and test

I am getting blocked like I expected! The problem is that I’m coming from my 2.2.2.2 address. What could be the issue? Good thing I told the logs to be sent to stdout so let’s check them for 403s:

kubectl logs -f -n wordpress nginx-9cdf87f68-tss6x|grep 403
...
10.126.32.147 - - [20/Dec/2020:13:37:33 +0000] "GET /admin HTTP/1.1" 403 187 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 11_1_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/87.0.4280.88 Safari/537.36"
...

I see the problem! That is not my 2.2.2.2 address! That was my request though. It seems that I’m not getting the real IP of the client but instead internal IPs from the load balancer.

Enter the PROXY Protocol

For access control, I didn’t want to rely on the X-Forwarded-For header since it is something that comes from the client. This means that someone could spoof the headers to get around my control. In addition to that, the DigitalOcean load balancer does not send this header so it’s a moot point. DigitalOcean does provide the PROXY Procotol in it’s load balancers but not by default. The short explanation is that this protocol will send in the IP like I want but it requires some configuration. It’s either enable PROXY protocol or not as well and there is no mixing or matching.

Enabling the PROXY Protocol on the load balancer was easy. You simply enable it in the Settings of the load balancer.

It is very important to NOT enable this until Nginx was configured. Otherwise, the site would have gone down. I explain my specific configuration below, but you are also welcome to explore the Nginx documentation on the PROXY Protocol.

Configuring Nginx

In my Testing Out the Digital Ocean Container Registry article, I built nginx with the PROXY protocol capability by enabling the ngx_http_realip module. It was like I wrote that previous article after getting this all working….? With the module already enabled, it was pretty easy to simply update the configuration and go. I added the following line to my sever block:

        set_real_ip_from 10.126.32.0/24;

Just like that, I was good to go so I thought. I was now getting denied only sometimes. I checked the logs again to find out why:

kubectl logs -f -n wordpress nginx-9cdf87f68-tss6x
...
10.126.32.147 - - [20/Dec/2020:13:37:33 +0000] "GET /admin HTTP/1.1" 403 187 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 11_1_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/87.0.4280.88 Safari/537.36"
2.2.2.2 - - [20/Dec/2020:18:35:49 +0000] "POST /admin HTTP/1.1" 200 98 "https://blog.shellnetsecurity.com/wp-admin/post.php?post=93&action=edit" "Mozilla/5.0 (Macintosh; Intel Mac OS X 11_1_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/87.0.4280.88 Safari/537.36"
3.3.3.3 - - [20/Dec/2020:13:37:33 +0000] "GET /admin HTTP/1.1" 403 187 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 11_1_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/87.0.4280.88 Safari/537.36"
...

Let’s chat about the set_real_ip_from statement. We need to add this statement for all potential IP addresses that we trust to provide us with the real client IP. In my case, it turned out that 10.126.32.0/24 was not a large enough block for the internal IP addresses so I needed to change that to a /16. Also, notice the 3.3.3.3 address? That’s the external IP of one of nodes in the kubernetes cluster. Armed with that knowledge, I expanded my server block to include multiple set_real_ip_from statements:

        set_real_ip_from 10.126.32.0/16;
        set_real_ip_from 3.3.3.3;
        set_real_ip_from 4.4.4.4;
        set_real_ip_from 5.5.5.5;

I reloaded everything and tested again and success every time! I got denied when I wasn’t on my 1.1.1.1 or 2.2.2.2 address. I also see others getting denied as well. When I’m sitting on 1.1.1.1 or 2.2.2.2, I’m able to get into my WordPress admin!

Disclosure: I have included some affiliate / referral links in this post. There’s no cost to you for accessing these links but I do indeed receive some incentive for it if you buy through them.

The house use to be full of random computers and networking gear but I’ve reduced the home presence over the years. I’ve messed with a number of cloud providers both inexpensive and expensive. My base for the majority of my toys reside in Digital Ocean. I’ve really liked what they’ve done over the years. Recently, they announced a Container Registry. If you follow this blog, then you remember my post, Posting a Custom Image to Docker Hub. In that post, I explained how to build an image and push it up Docker Hub. Some images might not need to be public for whatever the reason. Needless to say, Digital Ocean’s Container Registry announcement, intrigued me. With the move to WordPress, I figured that I should also build a custom nginx build to run in my Kubernetes cluster on Digital Ocean.

Building the Custom Nginx

This part was pretty easy. I simply created a Dockerfile for the build.

FROM ubuntu

ENV DEBIAN_FRONTEND noninteractive

MAINTAINER Scott Algatt

RUN apt-get update \
    && apt-get install -y libjansson-dev libcurl4-openssl-dev libapr1-dev libaprutil1-dev libssl-dev build-essential devscripts libtool m4 automake pkg-config libpcre3-dev zlib1g-dev\
    && apt -y upgrade \
    && apt -y autoremove \
    && apt-get clean \
    && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/* \
    && curl -o /tmp/nginx.tgz http://nginx.org/download/nginx-1.18.0.tar.gz

WORKDIR /tmp

RUN tar zxf nginx.tgz \
    && cd nginx-1.18.0 \
    && ./configure --with-http_realip_module\
    && make \
    && make install

EXPOSE 80
CMD ["/usr/local/nginx/sbin/nginx"]

As you can see from the Dockerfile, this is a really super simple build. It is also not very custom aside from my compile command where I’ve added –with-http_realip_module. This little addition is something that I will use later in a future post (I know everything will be in the future) but you can see what it does by visiting the nginx documentation. Anyhow, there you go. Aside from the configure command, I’m just setting up ubuntu to compile code and I download nginx and compile it. Then expose port 80 and run nginx.

Once you have created the Dockerfile, you can run a build to generate your docker image. You’ll see that my build command tags the build with a name, c-core-nginx, and specific version, 1.1. I would suggest doing this to help keep versions straight in your repository.

% docker build -t c-core-nginx:1.1 .
Sending build context to Docker daemon  21.72MB
Step 1/9 : FROM ubuntu
 ---> 4e2eef94cd6b
Step 2/9 : ENV DEBIAN_FRONTEND noninteractive
 ---> Using cache
 ---> decc285ce9e4
Step 3/9 : MAINTAINER Scott Algatt
 ---> Using cache
 ---> 197e4c81b654
Step 4/9 : RUN apt-get update     && apt-get install -y libjansson-dev libcurl4-openssl-dev libapr1-dev libaprutil1-dev libssl-dev build-essential devscripts libtool m4 automake pkg-config libpcre3-dev zlib1g-dev    && apt -y upgrade     && apt -y autoremove     && apt-get clean     && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*     && curl -o /tmp/nginx.tgz http://nginx.org/download/nginx-1.18.0.tar.gz
 ---> Using cache
 ---> d5c8a70c412f
Step 5/9 : COPY ./perimeterx-c-core /tmp/perimeterx-c-core
 ---> Using cache
 ---> d325026c19b6
Step 6/9 : WORKDIR /tmp
 ---> Using cache
 ---> 8fb23db246a3
Step 7/9 : RUN tar zxf nginx.tgz     && cd nginx-1.18.0     && ./configure --add-module=/tmp/perimeterx-c-core/modules/nginx --with-threads --with-http_realip_module    && make     && make install
 ---> Using cache
 ---> 25af69d04a9f
Step 8/9 : EXPOSE 80
 ---> Using cache
 ---> e74b4cc64160
Step 9/9 : CMD ["/usr/local/nginx/sbin/nginx"]
 ---> Using cache
 ---> 6f10e3bebefc
Successfully built 6f10e3bebefc
Successfully tagged c-core-nginx:1.1

After the build completes, you can confirm that your image is listed on your local docker repo

% docker images c-core-nginx
REPOSITORY     TAG       IMAGE ID       CREATED       SIZE
c-core-nginx   1.1       6f10e3bebefc   2 weeks ago   584MB
c-core-nginx   1.0       b3673b4bf518   2 weeks ago   584MB

Pushing Your Image to the Container Registry

I’m not going to spend a ton of effort in this section because the Digital Ocean Container Registry announcement I posted above explains the setup really well. At a high level, you simply complete the following steps:

1. Install and configure doctl (assuming you had never done this like me)
2. Login into your Digital Ocean account
3. Go to the Container Registry link
4. Create the Container Registry
5. Login to your registry using the doctl command
6. Push your desired container(s) to the registry

The below image shows a screenshot of my c-core-nginx images that I uploaded to my Container Registry.

Notice something really cool? The size of those images in my local registry is 584MB but they are roughly 194MB when uploaded. They are being compressed in the registry. This is a really nice feature since the initial free tier of Digital Ocean’s Container Registry is a single repo of 500MB.

In the future, you will see how I actually used this new feature for fun and zero profit.