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Kubernetes Agent + Ingress Controller + Module

access_time Updated Jun 20, 2021

Introduction

In this example, the Signal Sciences agent is installed as a Docker sidecar, communicating with a Signal Sciences native module for NGINX installed on an ingress-nginx Kubernetes ingress controller.

Integrating the Signal Sciences Agent

The Signal Sciences Agent can be installed as a sidecar into each pod or as a service for some specialized needs. The recommended way of installing the Signal Sciences Agent in Kubernetes is by integrating the sigsci-agent into a pod as a sidecar. This just means adding the sigsci-agent as an additional container to the Kubernetes pod. As a sidecar, the agent will scale with the app/service in the pod instead of having to do this separately. However, in some situations, it may make more sense to install the sigsci-agent container as a service and scale it separately from the application. The sigsci-agent container can be configured in various ways depending on the installation type and module being used.

Getting and Updating the Signal Sciences Agent Container Image

The official signalsciences/sigsci-agent container image available from the Signal Sciences account on Docker Hub is the recommended place to get the image. If you want to build your own image or need to customize the image, then follow the sigsci-agent build instructions.

The documentation references the latest version of the agent with imagePullPolicy: Always which will pull the latest agent version even if one already exist locally. This is so the documentation does not fall out of date and anyone using this will not have an agent that stays stagnant, however this may not be what if you need to keep installations consistent or on a specific version of the agent. In this case you should specify a version. Images on Docker Hub are tagged with their versions and a list of versions is available on Docker Hub.

Whether you choose to use the latest image or a specific version, there are a few items to consider to keep the agent up-to-date:

Using the latest Signal Sciences Container Image

If you do choose to use the latest image, then you want to consider how you will keep the agent up-to-date. If you have used the imagePullPolicy: Always option, then the latest image will be pulled on each startup and your agent will continue to get updates. To keep some consistency, you may instead choose to manually update the local cache by periodically forcing a pull instead of always pulling on startup.

docker pull signalsciences/sigsci-agent:latest

Then, use latest with imagePullPolicy: Never set in the configuration so that pulls are never done on startup (only manually as above):

- name: sigsci-agent
   image: signalsciences/sigsci-agent:latest
   imagePullPolicy: Never
   ...

Using a Versioned Signal Sciences Container Image

To use a specific version of the agent, then just replace latest with the agent version. You may also want to change imagePullPolicy: IfNotPresent in this case as the image should not change.

- name: sigsci-agent
   image: signalsciences/sigsci-agent:4.1.0
   imagePullPolicy: IfNotPresent
   ...

This will pull the specified agent version and cache it locally. If you use this method, then it is recommended that you parameterize the agent image, using Helm or similar, so that it is easier to update the agent images later on.

Using a Custom Tag for the Signal Sciences Container Image

It is also possible to apply a custom tag to a local agent image. To do this, pull the agent image (by version or use the latest), apply a custom tag, then use that custom tag in the configuration. You will want to specify imagePullPolicy: Never so that local images are only updated manually. You will need to periodically update the local image to keep the agent up-to-date.

For example:

docker pull signalsciences/sigsci-agent:latest
docker tag signalsciences/sigsci-agent:latest signalsciences/sigsci-agent:testing

Then use this image tag in the configuration:

- name: sigsci-agent
   image: signalsciences/sigsci-agent:testing
   imagePullPolicy: Never
...

Configuring the Signal Sciences Agent Container

Agent configuration is normally done via the environment. Most configuration options are available as environment variables. Environment variables names have the configuration option name all capitalized, prefixed with SIGSCI_ and any dashes (-) changed to underscores (_) (e.g., the max-procs option would become the SIGSCI_MAX_PROCS environment variable). For more details on what options are available, see the Agent Configuration documentation.

The sigsci-agent container has a few required options that need to be configured:

  • Agent credentials (ID and secret key)
  • A volume to write temporary files

Agent Credentials

The sigsci-agent credentials are configured with two environment variables. These variables must be set or the agent will not start.

  • SIGSCI_ACCESSKEYID: Identifies the site that the agent is configured against
  • SIGSCI_SECRETACCESSKEY: The shared secret key to authenticate and authorize the agent

The credentials can be found by following these steps:

  1. Log into the Signal Sciences console
  2. Go to Agents Configurations “Configurations Menu”
  3. On the Agents page click “View Agent Keys”
  4. Copy down the Access Key and Secret Key as this will be used later agent-keys “Agent Keys”

Because of the sensitive nature of these values, it is recommended to use the builtin secrets functionality of Kubernetes. With this configuration, the agent will pull the values from the secrets data instead of reading hardcoded the values into the deployment configuration. This also makes any desired agent credential rotation easier to manage by having to change them in only one place.

Using secrets via environment variables is done using the valueFrom option instead of the value option such as follows:

env:
 - name: SIGSCI_ACCESSKEYID
   valueFrom:
     secretKeyRef:
       # Update "my-site-name-here" to the correct site name or similar identifier
       name: sigsci.my-site-name-here
       key: accesskeyid
 - name: SIGSCI_SECRETACCESSKEY
   valueFrom:
     secretKeyRef:
       # Update "my-site-name-here" to the correct site name or similar identifier
       name: sigsci.my-site-name-here
       key: secretaccesskey

The secrets functionality keeps secrets in various stores in Kubernetes. This documentation uses the generic secret store in its examples, however any equivalent store can be used. Agent secrets can be added to the generic secret store with something like the following YAML:

apiVersion: v1
kind: Secret
metadata:
  name: sigsci.my-site-name-here
stringData:
  accesskeyid: 12345678-abcd-1234-abcd-1234567890ab
  secretaccesskey: abcdefg_hijklmn_opqrstuvwxy_z0123456789ABCD

This can also be created from the command line with kubectl such as with the following:

kubectl create secret generic sigsci.my-site-name-here \
  --from-literal=accesskeyid=12345678-abcd-1234-abcd-1234567890ab \
  --from-literal=secretaccesskey=abcdefg_hijklmn_opqrstuvwxy_z0123456789ABCD

See the documentation on secrets for more details.

Agent Temporary Volume

For added security, it is recommended that the sigsci-agent container be executed with the root filesystem mounted read only. The agent, however, still needs to write some temporary files such as the socket file for RPC communication and some periodically updated files such as GeoIP data. To accomplish this with a read only root filesystem, there needs to be a writeable volume mounted. This writeable volume can also be shared to expose the RPC socket file to other containers in the same pod. The recommended way of creating a writeable volume is to use the builtin emptyDir volume type. Typically this is just configured in the volumes section of a deployment.

volumes:
 - name: sigsci-tmp
   emptyDir: {}

Containers would then typically mount this volume at /sigsci/tmp:

volumeMounts:
 - name: sigsci-tmp
   mountPath: /sigsci/tmp

The default in the official agent container image is to have the temporary volume mounted at /sigsci/tmp. If this needs to be moved for the agent container, then the following agent configuration options should also be changed from their defaults to match the new mount location:

  • rpc-address defaults to /sigsci/tmp/sigsci.sock
  • shared-cache-dir defaults to /sigsci/tmp/cache

Integrating the Signal Sciences Agent into an Ingress Controller

In addition to installing Signal Sciences per application, it is also possible install Signal Sciences into a Kubernetes ingress controller that will receive all external traffic to your applications. Doing this is similar to installing into an application with a Signal Sciences module.

You must:

  • Install and configure the Signal Sciences Module into the ingress controller
  • Add the sigsci-agent container to the ingress pod and mount a sigsci-agent volume
  • Add an emptyDir{} volume as a place for the sigsci-agent to write temporary data

Kubernetes Nginx Ingress Controller

The Kubernetes Nginx Ingress Controller is an nginx based implementation for the ingress API. Signal Science supports a native module for nginx. This enables you to easily wrap the existing ingress-nginx controller to install the Signal Science module.

Wrap the Base nginx-ingress-controller to Install the Signal Science Module

Wrapping the nginx-ingress-controller is done by using the base controller and installing the Signal Sciences native nginx module. An example can be found here.

A prebuilt container can be pulled from Docker Hub with: docker pull signalsciences/sigsci-nginx-ingress-controller:0.30.0

The nginx ingress controller is installed with the mandatory.yaml file. This file contains a modified template of the Generic Ingress Controller Deployment as described at https://kubernetes.github.io/ingress-nginx/deploy/#prerequisite-generic-deployment-command. The main additions are:

Changing the ingress container to load the custom Signal Sciences Module/ingress container and adding Volume mounts for socket file communication between the Module/ingress container and Agent sidecar container:

...
    containers:
      - name: nginx-ingress-controller
        image: signalsciences/sigsci-nginx-ingress-controller:0.30.0
        ...
        volumeMounts:
          - name: sigsci-tmp
            mountPath: /sigsci/tmp
...

Loading the Signal Sciences Module in nginx.conf via ConfigMap:

kind: ConfigMap
apiVersion: v1
data:
  main-snippet: load_module /usr/lib/nginx/modules/ngx_http_sigsci_nxo_module-1.17.7.so;
  http-snippet: sigsci_agent_host unix:/sigsci/tmp/sigsci.sock;
metadata:
  name: nginx-configuration
  namespace: ingress-nginx
  labels:
    app.kubernetes.io/name: ingress-nginx
    app.kubernetes.io/part-of: ingress-nginx

Adding a container for the Signal Sciences Agent:

...
    containers:
    ...
      # Signal Sciences Agent running in default RPC mode
      - name: sigsci-agent
        image: signalsciences/sigsci-agent:4.0.0
        imagePullPolicy: IfNotPresent
        env:
        - name: SIGSCI_ACCESSKEYID
          valueFrom:
            secretKeyRef:
              # This secret needs added (see docs on sigsci secrets)
              name: sigsci.my-site-name-here
              key: accesskeyid
        - name: SIGSCI_SECRETACCESSKEY
          valueFrom:
            secretKeyRef:
              # This secret needs added (see docs on sigsci secrets)
              name: sigsci.my-site-name-here
              key: secretaccesskey
        securityContext:
          # The sigsci-agent container should run with its root filesystem read only
          readOnlyRootFilesystem: true
        volumeMounts:
        # Default volume mount location for sigsci-agent writeable data (do not change mount path)
        - name: sigsci-tmp
          mountPath: /sigsci/tmp
...

And defining the volume used above:

...
      volumes:
      # Define a volume where sigsci-agent will write temp data and share the socket file,
      # which is required with the root filesystem is mounted read only
      - name: sigsci-tmp
        emptyDir: {}
...

Setup

  1. Set the name for the secrets for the agent keys in mandatory.yaml
...
            env:
            - name: SIGSCI_ACCESSKEYID
              valueFrom:
                secretKeyRef:
                  # This secret needs added (see docs on sigsci secrets)
                  name: sigsci.my-site-name-here
                  key: accesskeyid
            - name: SIGSCI_SECRETACCESSKEY
              valueFrom:
                secretKeyRef:
                  # This secret needs added (see docs on sigsci secrets)
                  name: sigsci.my-site-name-here
                  key: secretaccesskey
...
  1. Pull or build build the nginx ingress + Signal Sciences Module container. Set whatever registry & repository name you’d like here, just be sure to set the image to match in mandatory.yaml.
docker pull signalsciences/sigsci-nginx-ingress-controller:0.30.0
  1. Deploy using modified Generic Deployment
kubectl apply -f mandatory.yaml
  1. Create service to expose Ingress Controller

The steps necessary are dependent on your cloud provider. Official instructions can be found at https://kubernetes.github.io/ingress-nginx/deploy/#provider-specific-steps

Example:

apiVersion: extensions/v1beta1
kind: Ingress
metadata:
  name: test-ingress
  namespace: ingress-nginx
  annotations:
    nginx.ingress.kubernetes.io/rewrite-target: /
spec:
  rules:
  - http:
      paths:
      - path: /testpath
        backend:
          serviceName: nginx
          servicePort: 80