{"id":84,"date":"2025-12-20T07:04:48","date_gmt":"2025-12-20T07:04:48","guid":{"rendered":"https:\/\/steadyrabbit.in\/blogs\/?p=84"},"modified":"2025-12-20T07:04:48","modified_gmt":"2025-12-20T07:04:48","slug":"from-monolith-to-cap-carving-microservices-out-of-ecc-no-big-bang-required","status":"publish","type":"post","link":"https:\/\/steadyrabbit.in\/blogs\/from-monolith-to-cap-carving-microservices-out-of-ecc-no-big-bang-required\/","title":{"rendered":"From Monolith to CAP: Carving Microservices Out of ECC\u2014No Big-Bang Required"},"content":{"rendered":"\n

TL;DR\u00a0<\/h4>\n\n\n\n

Ripping out your ECC monolith in one epic weekend is the fastest path to CFO heartburn. A safer route is progressive carve-out<\/strong>: lift one business capability at a time into a Cloud Application Programming (CAP) microservice<\/strong> running on SAP BTP, connect it back to ECC with Event Mesh<\/strong>, and retire legacy code sprint by sprint. We share the exact playbook our Micro-GCC squad used to extract \u201cSales Pricing\u201d from 300 000 lines of Z-code\u2014with zero plant downtime<\/strong> and a 43 % latency improvement. All CDS, mta.yaml, and Terraform snippets included.<\/p>\n\n\n\n

Why \u201cLift-and-Shift\u201d Fails in SAP Land\u00a0<\/h4>\n\n\n\n

Typical big-bang plan:<\/em> clone ECC database, refactor Z-code in S\/4 sandbox, schedule 48-hour outage.
Reality:<\/em> transports collide, IDoc queues pile up, month-end close panics.<\/p>\n\n\n\n

Key blockers:<\/p>\n\n\n\n

    \n
  1. Elephant tables<\/strong> (MARA, VBAK) resist parallel updates.
    <\/li>\n\n\n\n
  2. Custom Z-code couples UI, business logic, and DB calls in one lump.
    <\/li>\n\n\n\n
  3. Cut-over windows for global plants must be < 15 min<\/strong>.
    <\/li>\n<\/ol>\n\n\n\n

    Progressive carve-out<\/strong> solves this by:<\/p>\n\n\n\n

      \n
    • Picking a well-bounded domain (\u201cSales Pricing\u201d).
      <\/li>\n\n\n\n
    • Creating a CDS model + CAP service<\/strong> in BTP.
      <\/li>\n\n\n\n
    • Publishing change events from ECC to Event Mesh.
      <\/li>\n\n\n\n
    • Gradually re-routing traffic\u2014no nuclear weekends.<\/li>\n<\/ul>\n\n\n\n

      Reference Architecture\u00a0<\/h4>\n\n\n\n

      sql<\/p>\n\n\n\n

      CopyEdit<\/p>\n\n\n\n

            ECC (Blue)          Event Mesh           BTP (Green)<\/p>\n\n\n\n

         +—————-+   +—————+   +——————+<\/p>\n\n\n\n

         |  SD Z_PRICING  |–>|  SD.PRICING.* |–>| CAP Service v1   |<\/p>\n\n\n\n

         | (ABAP Module)  |   +—————+   |  \/pricing\/* OData|<\/p>\n\n\n\n

         +—————-+                       +——————+<\/p>\n\n\n\n

              \u2191    |                                     \u2191<\/p>\n\n\n\n

              |    | SAP SLT (real-time)                 |<\/p>\n\n\n\n

              |    +————————————-+<\/p>\n\n\n\n

              |                                          <\/p>\n\n\n\n

         Legacy UI5 App           New UI5\/Fiori<\/p>\n\n\n\n

        \n
      • SLT<\/strong> replicates VBAK\/VBAP delta to HANA Cloud.
        <\/li>\n\n\n\n
      • CDS model<\/strong> maps to new HANA Cloud schema.
        <\/li>\n\n\n\n
      • CAP service<\/strong> (Node.js) exposes OData V4 for Fiori & external APIs.
        <\/li>\n\n\n\n
      • Event Mesh<\/strong> channels SD.PRICING.UPDATED messages; CAP subscribes and updates cache.
        <\/li>\n<\/ul>\n\n\n\n

        Step-switch<\/strong>: gateway route toggles \/pricing\/* to CAP when E2E tests green.<\/p>\n\n\n\n

        Step-by-Step Carve-Out\u00a0<\/h4>\n\n\n\n
        3.1 Scope the Domain<\/h5>\n\n\n\n

        Rule of thumb:<\/em> choose a business capability with \u2264 3 BAPIs<\/strong> and \u2264 5 tables<\/strong>.
        For Sales Pricing we touched VBAK, VBAP, KONV<\/strong> and three custom Z-tables.<\/p>\n\n\n\n

        \n\n\n\n
        3.2 Create CDS Model<\/h5>\n\n\n\n

        db\/schema.cds<\/p>\n\n\n\n

        cds<\/p>\n\n\n\n

        CopyEdit<\/p>\n\n\n\n

        namespace sd.pricing;<\/p>\n\n\n\n

        entity SalesOrder {<\/p>\n\n\n\n

          key SalesOrderID : String(10);<\/p>\n\n\n\n

          NetValue         : Decimal(15,2);<\/p>\n\n\n\n

          Currency         : String(5);<\/p>\n\n\n\n

        }<\/p>\n\n\n\n

        entity PricingCondition {<\/p>\n\n\n\n

          key CondID    : Integer;<\/p>\n\n\n\n

              SalesOrderID : Association to SalesOrder;<\/p>\n\n\n\n

              Amount       : Decimal(15,2);<\/p>\n\n\n\n

              CondType     : String(4);<\/p>\n\n\n\n

        }<\/p>\n\n\n\n

        Run:<\/p>\n\n\n\n

        bash<\/p>\n\n\n\n

        CopyEdit<\/p>\n\n\n\n

        cds deploy –to hana<\/p>\n\n\n\n

        \n\n\n\n
        3.3 Build CAP Service<\/h5>\n\n\n\n

        srv\/pricing-service.js<\/p>\n\n\n\n

        js<\/p>\n\n\n\n

        CopyEdit<\/p>\n\n\n\n

        module.exports = srv => {<\/p>\n\n\n\n

          const { SalesOrder, PricingCondition } = srv.entities<\/p>\n\n\n\n

          srv.before(‘CREATE’, PricingCondition, validateAmounts)<\/p>\n\n\n\n

          srv.on(‘reprice’, async req => {<\/p>\n\n\n\n

            const so = await SELECT.one.from(SalesOrder).where({ SalesOrderID: req.data.id })<\/p>\n\n\n\n

            \/\/ call external pricing engine, update NetValue \u2026<\/p>\n\n\n\n

            return so<\/p>\n\n\n\n

          })<\/p>\n\n\n\n

        }<\/p>\n\n\n\n

        mta.yaml adds requires: [ hana, eventmesh ].<\/p>\n\n\n\n

        \n\n\n\n
        3.4 Event Mesh Subscription<\/h5>\n\n\n\n

        event-mesh.json<\/p>\n\n\n\n

        json<\/p>\n\n\n\n

        CopyEdit<\/p>\n\n\n\n

        {<\/p>\n\n\n\n

          “source”: “ECC”,<\/p>\n\n\n\n

          “events”: [<\/p>\n\n\n\n

            { “name”: “SD.PRICING.UPDATED”, “namespace”: “sap.s4”, “version”: “v1” }<\/p>\n\n\n\n

          ]<\/p>\n\n\n\n

        }<\/p>\n\n\n\n

        CAP srv\/pricing-sub.js<\/p>\n\n\n\n

        js<\/p>\n\n\n\n

        CopyEdit<\/p>\n\n\n\n

        module.exports = srv => {<\/p>\n\n\n\n

          const { PricingCondition } = srv.entities<\/p>\n\n\n\n

          srv.on(‘sap.s4\/SD.PRICING.UPDATED’, async msg => {<\/p>\n\n\n\n

            await UPDATE(PricingCondition).where({CondID: msg.data.id}).set(msg.data)<\/p>\n\n\n\n

          })<\/p>\n\n\n\n

        }<\/p>\n\n\n\n

        Latency ECC \u2192 CAP cache: \u2264 300 ms<\/strong> (tested 95th percentile).<\/p>\n\n\n\n

        \n\n\n\n
        3.5 CI\/CD Pipeline<\/h5>\n\n\n\n

        jenkinsfile<\/p>\n\n\n\n

        groovy<\/p>\n\n\n\n

        CopyEdit<\/p>\n\n\n\n

        stage(‘Build’) { sh ‘mbt build’ }<\/p>\n\n\n\n

        stage(‘Deploy’) {<\/p>\n\n\n\n

          withCredentials([file(credentialsId: ‘btp.json’, variable: ‘BTPCRED’)]) {<\/p>\n\n\n\n

            sh ‘cf deploy mta_archives\/pricing_1.0.0.mtar –json’<\/p>\n\n\n\n

          }<\/p>\n\n\n\n

        }<\/p>\n\n\n\n

        stage(‘Smoke’) { sh ‘npm run smoke’ }<\/p>\n\n\n\n

        Smoke tests hit \/pricing\/$metadata plus \/reprice.<\/p>\n\n\n\n

        \n\n\n\n
        3.6 Route Traffic<\/h5>\n\n\n\n

        In SAP APIM:<\/p>\n\n\n\n

        yaml<\/p>\n\n\n\n

        CopyEdit<\/p>\n\n\n\n

        routes:<\/p>\n\n\n\n

          – match: \/pricing\/**<\/p>\n\n\n\n

            target: cap-green<\/p>\n\n\n\n

            weight: 20<\/p>\n\n\n\n

          – match: \/pricing\/**<\/p>\n\n\n\n

            target: ecc-blue<\/p>\n\n\n\n

            weight: 80<\/p>\n\n\n\n

        After 24 h of green logs, flip weights to 100\/0. Rollback = YAML revert.<\/p>\n\n\n\n

        Latency & Cost Benchmarks\u00a0<\/h4>\n\n\n\n
        Metric<\/strong><\/td>ECC Z-RFC<\/strong><\/td>CAP Microservice<\/strong><\/td><\/tr>
        p95 Read Latency<\/td>520 ms<\/td>297 ms<\/strong><\/td><\/tr>
        p95 Write Latency<\/td>640 ms<\/td>335 ms<\/strong><\/td><\/tr>
        Monthly Infra \u20ac<\/td>N\/A (on-prem)<\/td>\u20ac420<\/strong> (BTP, 2 GB HANA Cloud)<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

        Savings: dev hours (fewer OSS notes), faster user response, and clear path to mobile APIs.<\/p>\n\n\n\n

        Case Study Snapshot\u00a0<\/h4>\n\n\n\n

        Industrial OEM<\/em> needed real-time price quotes in a dealer portal.<\/p>\n\n\n\n

          \n
        • Before<\/strong>: RFC call chain through VPN \u2192 700 ms.
          <\/li>\n\n\n\n
        • After<\/strong>: CAP service directly exposed via BTP \u2192 310 ms.
          <\/li>\n\n\n\n
        • Outcome<\/strong>: dealer checkout conversion +8 %.
          <\/li>\n<\/ul>\n\n\n\n

          Z-code reduction: 48 000 lines deleted; ATC critical findings \u2013100 %.<\/p>\n\n\n\n

          Pitfalls & Pro-Tips\u00a0<\/h4>\n\n\n\n
          Pitfall<\/strong><\/td>Fix<\/strong><\/td><\/tr>
          CDS enum mismatch<\/td>Use @cds.odata.valuelist for domain values; sync with DDIC check table.<\/td><\/tr>
          Event duplicates<\/td>De-duplicate by message ID; CAP persists last processed offset.<\/td><\/tr>
          HANA Cloud memory spike<\/td>Partition KONV by fiscal year; purge archive years.<\/td><\/tr>
          Fiori app calls old RFC<\/td>Use UI5 cache buster; adjust destination to CAP SACF.<\/td><\/tr>
          Devs fear CAP learning curve<\/td>Scaffold service with yeoman-generator-cap-project\u20145 min ramp.<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

          Adoption Roadmap\u00a0<\/h4>\n\n\n\n
          Sprint<\/strong><\/td>Milestone<\/strong><\/td><\/tr>
          1<\/td>Enable abapGit, export domain package<\/td><\/tr>
          2<\/td>Define CDS & deploy to HANA Cloud<\/td><\/tr>
          3<\/td>Build CAP service & Event Mesh subscription<\/td><\/tr>
          4<\/td>20 % canary traffic via APIM<\/td><\/tr>
          5<\/td>Full cut-over; retire old Z-code package<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

          Repeat domain by domain until ECC monolith collapses into modular CAP landscape.<\/p>\n\n\n\n

          Take-Home Checklist\u00a0<\/h4>\n\n\n\n
            \n
          1. Pick a self-contained domain (\u2264 5 tables).
            <\/li>\n\n\n\n
          2. Model CDS + deploy to HANA Cloud.
            <\/li>\n\n\n\n
          3. Build CAP OData service; subscribe to Event Mesh.
            <\/li>\n\n\n\n
          4. Canary route 20 % traffic; monitor p95 latency.
            <\/li>\n\n\n\n
          5. Delete Z-code after success\u2014win back predictability.<\/li>\n<\/ol>\n","protected":false},"excerpt":{"rendered":"

            TL;DR\u00a0 Ripping out your ECC monolith in one epic weekend is the fastest path to CFO heartburn. A safer route is progressive carve-out: lift one business capability at a time into a Cloud Application Programming (CAP) microservice running on SAP BTP, connect it back to ECC with Event Mesh, and retire legacy code sprint by […]<\/p>\n","protected":false},"author":1,"featured_media":15,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[5],"tags":[],"class_list":["post-84","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-sap-modernization"],"_links":{"self":[{"href":"https:\/\/steadyrabbit.in\/blogs\/wp-json\/wp\/v2\/posts\/84","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/steadyrabbit.in\/blogs\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/steadyrabbit.in\/blogs\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/steadyrabbit.in\/blogs\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/steadyrabbit.in\/blogs\/wp-json\/wp\/v2\/comments?post=84"}],"version-history":[{"count":1,"href":"https:\/\/steadyrabbit.in\/blogs\/wp-json\/wp\/v2\/posts\/84\/revisions"}],"predecessor-version":[{"id":85,"href":"https:\/\/steadyrabbit.in\/blogs\/wp-json\/wp\/v2\/posts\/84\/revisions\/85"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/steadyrabbit.in\/blogs\/wp-json\/wp\/v2\/media\/15"}],"wp:attachment":[{"href":"https:\/\/steadyrabbit.in\/blogs\/wp-json\/wp\/v2\/media?parent=84"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/steadyrabbit.in\/blogs\/wp-json\/wp\/v2\/categories?post=84"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/steadyrabbit.in\/blogs\/wp-json\/wp\/v2\/tags?post=84"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}