Using two database connections (with separate db connection pools) with Duct.

config.edn

{:duct.profile/base
 {:duct.core/project-ns project-ns

  [:duct.database.sql/hikaricp :duct.database.sql.hikaricp/postgres]
  {:jdbc-url #duct/env ["JDBC_POSTGRES_URL" Str]
   :minimum-idle 10
   :maximum-pool-size 25
   ;; Other HikariCP options go here.
   }

  [:project-ns.boundary.adapter.persistence/sql :project-ns.boundary.adapter.persistence.sql/postgres]
  #ig/ref :duct.database.sql.hikaricp/postgres

  [:duct.database.sql/hikaricp :duct.database.sql.hikaricp/sqlserver]
  {:jdbc-url #duct/env ["JDBC_SQLSERVER_URL" Str]
   :minimum-idle 10
   :maximum-pool-size 25
   ;; Other HikariCP options go here.
   }

  [:project-ns.boundary.adapter.persistence/sql :project-ns.boundary.adapter.persistence.sql/sqlserver]
  #ig/ref :duct.database.sql.hikaricp/sqlserver

  [:duct/const :project-ns/common-config] {:db-postgres  #ig/ref :project-ns.boundary.adapter.persistence.sql/postgres
                                           :db-sqlserver #ig/ref :project-ns.boundary.adapter.persistence.sql/sqlserver
                                           ;; More config options go here.
                                           }

  :project-ns.api/user #ig/ref :project-ns/common-config
  :project-ns.api/device #ig/ref :project-ns/common-config

  ;; Other Intengrant keys go here.

  } ;; Base profile ends here

 :duct.profile/dev #duct/include "dev"
 :duct.profile/local #duct/include "local"
 :duct.profile/prod {}

 ;; More Duct modules and profiles go here.

}

connector.clj

(ns project-ns.boundary.adapter.persistence.connector)

(defrecord Sql [spec])

sql.clj

(ns project-ns.boundary.adapter.persistence.sql
  (:require [project-ns.boundary.adapter.persistence.connector :as connector]
            
            ;; Other namespaces that implement different protocols on the
            ;; `connector/Sql` record type go here.
            
            [integrant.core :as ig]))

(defmethod ig/init-key :project-ns.boundary.adapter.persistence/sql [_ {:keys [spec]}]
  (connector/->Sql spec))