Continuous Deployment API Pipeline

This blogpost explains our CD (Continuous Deployment) pipeline, use it for your own convenience and as always tips and remarks are welcome!

We're using the Kong API Gateway to handle all the REST and SOAP calls to middleware and back-end (micro-)services.

Each API should be described as an Open API Specification file, with all the details of the API, Kong plugins and in case it's a REST service also the request and response schema's.

All these Open API Specifications (OAS files) are stored in our on-premise Gitlab Repository server, combined with a Gitlab Runners (agents) server to execute the pipelines for deployment.

Now let me describe our pipeline set-up, it consists of eight steps:

1.     Get the Open API Specification

2.     Validate the Open API Specification

3.     Generate the Kong decK file

4.     Replace project specific variables

5.     Validate Kong decK file

6.     Synchronize (deploy) Kong artefacts

7.     Remove Kong plugins from Open API Specification

8.     Deploy Open API Specification to Portal or API Marketplace/Platform

An API Project in Gitlab consists of the pipeline (.gitlab-ci.yml file), which includes file variables.yml and the actual pipeline in Project "library" and thirdly the API Design (OAS).

The OAS is either a yml file in the Gitlab project specified in file variables.yml or included in the Insomnia project in directory .insomnia. With Insomnia 2023.5.8 our teams can still Git Sync for free.

Step 1) Get the OAS, either variable OAS is present in file variables.yml or it's exported from Insomnia executing inso export spec within docker image kong-inso-8.4.5.

Results from this step are the oas spec name and the actual oas.yml file.

Step 2) Validate OAS, within docker image stoplight/spectral we download using curl the .spectral.yml ruleset from our library project and execute spectral lint.

Our .spectral.yml extends: [[spectral:oas, all], [spectral:asyncapi, all]] and we've added some specific errors, like:

• we need contact name and email present, email should be a company email address
• the oas file need x-kong-plugin-application-registration present with value auto_approve set to false

Step 3) Generate Kong decK (decK is derived from the combination of words ‘declarative’ and ‘Kong’) file within docker image kong-deck-1.36.1, after creating decK file we set the service protocol, host and port from environment specific variables in variables.yml file, and we add the project tag:

only:
- development
script:
- deck file openapi2kong --inso-compatible -s oas.yaml -o kong.yaml
- deck file patch -s kong.yaml -o kong.yaml --selector="$..services[*]" --value='protocol:"'"$DEV_PROTOCOL"'"'
- deck file patch -s kong.yaml -o kong.yaml --selector="$..services[*]" --value='host:"'"$DEV_HOST"'"'
- deck file patch -s kong.yaml -o kong.yaml --selector="$..services[*]" --value='port:'$DEV_PORT''
- deck file add-tags -s kong.yaml -o kong.yaml $projectname

Some years ago we were adding upstream with targets, but as we have a dedicated load balancer we don't need Kong to balance over targets, also setting endpoint on service gives better overview of upstream systems in Kong Manager.

Step 4) If the decK file contains project specific placeholders which should be replaced by environment specific values we add replace steps to the project .gitlab-ci.yml file.

The replacements can be done with simple linux commands within basic docker image linux-alpine-3.18.

Step 5) DecK validation, this step validates the Kong decK file within image kong-deck-1.36.1, executing both deck gateway validate and deck gateway diff.

We noticed that if a service has an existing application_instance and service is renamed this leads to deletion of old and creation of new service, validation step will pass but sync fails due to existing reference.

Step 6) Synchronize (deploy) to Kong, executing deck gateway sync within docker image kong-deck-1.36.1

Step 7) As the OAS contains Kong specific plugins that we don't want to expose in the Developer Portal, or any API Platform, we remove all the plugins.

For now we use hashtags within the OAS to specify begin and end of a plugin, using linux script within docker image linux-alpine-3.18 to remove everything between and including the hashtags.

In the future we might add smarter plugin removal using yq, as Kong plugins are well defined objects starting with x-kong-plugin.

Step 8) Using docker image linux-alpine-3.18 with curl included we can post the censored OAS to our Developer Portal.

Time for a small example, see the following snapshot of a single API design, where there is a single path on Kong: /orders with the following rules:

• If the optional HTTP Header field X-Order-Version contains v2 the request should be routed to upstream system ORDER_V2_HOST with path v2
  
• Else the request should be routed to default upstream system with path v1

This can be achieved with different projects/OAS, but sometimes this is requested within the same spec:

paths:
  /orders:
    get:
#BEGIN_KONG_PLUGINS_1
      x-kong-plugin-request-transformer-advanced:
        name: request-transformer-advanced
        config:
          replace:
            uri: /v1/orders
#END_KONG_PLUGINS_1
...
#BEGIN_KONG_PLUGINS_2
  /orders[REMOVEME]:
    get:
      x-kong-route-defaults:
        headers:
          X-Order-Version:
          - v2
      x-kong-plugin-route-transformer-advanced:
        name: route-transformer-advanced
        config:
          host: ORDER_V2_HOST
          path: /v2/orders
#END_KONG_PLUGINS_2

This OAS is valid in all OAS editors like Insomnia, Swagger etc.

The duplicated path is extended with [REMOVEME] to make the design a valid Open API Specification. After creating the decK file this [REMOVEME] will be removed in step 4. The resulted decK file remains valid for Kong and contains identical paths but with different HTTP Header configuration. ORDER_V2_HOST is an environment specific placeholder which is replaced in step 4 by the value set in variables.yml.

In step 6 the service is deployed to Kong.

In step 7 the script removes everything between #BEGIN_KONG_PLUGINS_1 and #END_KONG_PLUGINS_1 which is the Kong plugin changing the upstream uri. Also everything between #BEGIN_KONG_PLUGINS_2 and #END_KONG_PLUGINS_2 is removed, which is the duplicated path.
Removal includes the lines starting with #, including additional comments starting with #.

After deployment in step 8 the result is a single path visible in the design on the Developer Portal. The API consumers won't see the upstream systems and the technical routing based on X-Order-Version. Surely the HTTP Header X-Order-Version should be described as an optional header field with it's purpose.