Named map template for a routing static map

template.json

{
    "auth": {
      "method": "open"
    },
    "version": "0.0.1",
    "name": "teradata_uk",
    "placeholders": {
      "postcode1": {
        "type": "sql_ident",
        "default": "M40"
      },
      "postcode2": {
        "type": "sql_ident",
        "default": "WC2N"
      }
    },
    "layergroup": {
      "version": "1.0.1",
      "layers": [
        {
          "type": "http",
          "options": {
            "urlTemplate": "http://{s}.basemaps.cartocdn.com/light_nolabels/{z}/{x}/{y}.png",
            "subdomains": "abcd"
          }
        },
        {
          "type": "cartodb",
          "options": {
            "sql": "WITH point1 as (SELECT cdb_geocode_postalcode_point(<%= postcode1 %>, 'UK') as geo ), point2 as (SELECT cdb_geocode_postalcode_point(<%= postcode2 %>, 'UK') as geo ), route AS (SELECT r.shape as geo, r.length FROM point1, point2, cdb_route_point_to_point(point1.geo, point2.geo, 'car') r ) SELECT 3 as cartodb_id, ST_Transform(geo,3857) as the_geom_webmercator, to_char(length::real, '999,999 km') as label FROM route UNION ALL SELECT 1 as cartodb_id, ST_Transform(geo,3857) as the_geom_webmercator, 'From ' || <%= postcode1 %> as label FROM point1 UNION ALL SELECT 2 as cartodb_id, ST_Transform(geo,3857) as the_geom_webmercator, 'To ' || <%= postcode2 %> as label FROM point2 ",
            "layer_name": "route",
            "cartocss": "#layer['mapnik::geometry_type'=1] {marker-width: 15; marker-fill: #FFB927; marker-fill-opacity: 0.9; marker-line-color: #ffda8d; marker-line-width:  1.5; marker-line-opacity: 1; marker-placement: point; marker-type: ellipse; marker-allow-overlap: true; } #layer['mapnik::geometry_type'=2] {line-width: 9; line-color: #3EBCAE; line-opacity: .7; } #layer::labels {text-name: [label]; text-face-name: 'DejaVu Sans Book'; text-size: 15; text-fill: #343A40; text-label-position-tolerance: 0; text-halo-radius: 1; text-halo-fill: #FFFFFF; text-dy: -10; text-allow-overlap: true; text-placement: point; text-placement-type: dummy; } ",
            "cartocss_version": "2.1.1",
            "interactivity": [
              "cartodb_id",
              "name"
            ],
            "table_name": "route",
            "attributes": {}
          }
        }
      ]
    },
    "view": {
      "zoom": 6,
      "center": {
        "lng": -3.6, 
        "lat": 54.97
      },
      "bounds": {
        "west" : -10.17,
        "south":  49.92,
        "east" :   2.90,
        "north":  59.47
      } 
    }
}