About delegation

As your environment grows, your gateways manage traffic for more and more routes. You might also have more ways of routing to a particular path for an app. To organize all your routes, you can use route table delegation. Delegation means that the routing decision for a route in one table instead gets made by another table.

  • “Parent” or “root” route table: The route table that delegates requests to another route table. This route table often configures the host and matching gateway details so that the routes in all the sub-tables are exposed on the same host. You can also configure the sorting method, such as by weight or specificity.
  • “Child” or “sub” route table: The route table that fulfills the routing request. This sub-table has the routing rules to match and forward traffic to the backing service.

This approach gives you the flexibility to manage a large number of routes in several ways, such as with label and matcher inheritance.

Label inheritance: Routes can inherit labels of their own route table, as well as their parent route table. This way, you can apply the same labels to many routes at once. Then, you can use these labels to select the routes in other resources, such as to apply security policies. For more information, see Route label inheritance.

Matcher inheritance: Routes also inherit matchers from the parent route table. This way, you can route to specific subpaths that share a common element. For more information, see Route matcher inheritance.

For more information, review the following documentation:

Delegate to child route tables based on weight

Delegate routing to sub-tables based on an assigned order. Individual routes are kept in the order that they appear relative to their tables, but tables are sorted by the weight that you assign to them. When a service in your mesh sends a request to another service, the request is matched against the routes in the highest-weighted route table first. If the request doesn’t match a route in the first sub-table, it is matched against the routes in the second-highest-weighted table, and so on.

  1. Follow the guides in Forward requests to a destination to set up each route table that you want to include in this sub-table set. For each route table, include the following additional settings for delegation:

    • In the spec section, do not include the hosts or workloadSelectors fields. The parent route table dictates these fields instead.
    • In the spec section, add the weight field to indicate route table priority. Higher integer values indicate a higher priority in the list of sub-tables. Note that tables of the same weight stay in the same order that you list them in the parent route table, which is the list order when you specify sub-tables by name, or the creation timestamp when you select sub-tables by label.
    • Optional: If you want to refer to the sub-tables by label rather than by table name, add a label in the metadata section. Be sure to use the same label for each sub-table.
    • Example: Say that you are testing multiple types of request matching for myapp. You define two different route tables, one for each type of matching, and label them as table: myapp. You assign a higher weight to the table that uses prefix matching to test that matching method now, and a lower weight to the table that uses query parameters to focus on that later. Your sub-tables might look like the following configurations:
      apiVersion: networking.gloo.solo.io/v2
kind: RouteTable
metadata:
  name: prefix-match
  namespace: global
  # Label for the sub-table set
  labels:
    table: myapp
spec:
  # Higher weight means first priority in the sub-table order
  weight: 100
  http:
  # Table routes any requests to 'myapp.global.svc.cluster.local/myapp/.*'
  - matchers:
    - uri:
        prefix: /myapp
        ignoreCase: true
    forwardTo:
      destinations:
      - ref:
          name: myapp
          namespace: global
          cluster: ${CLUSTER_NAME}
        port:
          number: 8090
        kind: SERVICE
---
apiVersion: networking.gloo.solo.io/v2
kind: RouteTable
metadata:
  name: query-parameters-match
  namespace: global
  # Label for the sub-table set
  labels:
    table: myapp
spec:
  # Lower weight means second priority in the sub-table order
  weight: 90
  http:
  # Table routes any requests to 'myapp.global.svc.cluster.local/myapp/.*?version=stage'
  - matchers:
    - uri:
        prefix: /myapp
    - queryParameters:
      - name: version
        value: stage
    forwardTo:
      destinations:
      - ref:
          name: myapp
          namespace: global
          cluster: ${CLUSTER_NAME}
        port:
          number: 8090
        kind: SERVICE

  2. Create the parent route table to delegate requests based on sub-table weight. In this example parent table, requests to the myapp.global.svc.cluster.local host are delegated to sub-tables with the table: myapp label, based on the order created by table weights. Note that you can also specify the sub-table names instead of the label by using the routeTables.name field.

      kubectl apply --context $REMOTE_CONTEXT1 -n global -f- <<EOF
apiVersion: networking.gloo.solo.io/v2
kind: RouteTable
metadata:
  name: delegate-weight
  namespace: global
spec:
  hosts:
    - 'myapp.global.svc.cluster.local'
  http:
  - delegate:
      # Selects tables based on label
      routeTables:
        - labels:
            table: myapp
      # Delegates based on order of weights
      sortMethod: TABLE_WEIGHT
EOF

  3. Test route table delegation by accessing the host and any necessary request-matching criteria.

    • For example, log in to an app in your mesh and send a request to http://myapp:9080/myapp/foo to verify that the request is routed to the prefix-matching route in the prefix-match sub-table.
    • You might also change the weights for the sub-tables to test that order instead, such as putting the query-parameters-match sub-table higher in the order. Then, you can log in to an app in your service mesh and send a request to http://myapp:9080/myapp/foo?version=stage to verify that the request is routed to the query parameter-matching route in the query-parameters-match sub-table.

Delegate to child route tables based on route specificity

When an incoming request to a host arrives at the ingress gateway, the gateway processes all routes in each sub-table that you select. By default, routes are sorted by table weight. However, you can change the sorting method to sort by specificity instead. Then, the resulting routes are sorted by specificity to reduce the chance that a general route short-circuits a more specific route.

The following specificity rules apply:

  • Exact path matchers are considered more specific than regex path matchers, which are more specific than prefix path matchers.
  • Matchers of the same type are sorted by length of the path in descending order.
  • Only the most specific matcher on each route is used.
  • In the event of a sort tie, table weights are used across sub-tables, and route order is used within sub-tables.

For example, consider the following two sub-tables that are sorted by specificity and the resulting route list.

  • Sub-table A, with a table weight of 1 in case of sort ties:
    • prefix: /foo
    • prefix: /foo/more/specific
    • prefix: /foo/even/more/specific
    • exact: /foo/exact
    • exact: /foo/another/exact
    • regex: /foo/*
    • regex: /fooo/*
  • Sub-table B, with a table weight of 2:
    • prefix: /bar
    • prefix: /bar/more/specific
    • prefix: /bar/even/more/specific
    • exact: /bar/exact
    • regex: /bar/*

The resulting routes are sorted in this order:

  • exact: /foo/another/exact
  • exact: /bar/exact
  • exact: /foo/exact
  • regex: /bar/*
  • regex: /foo/*
  • regex: /fooo/*
  • prefix: /bar/even/more/specific
  • prefix: /foo/even/more/specific
  • prefix: /bar/more/specific
  • prefix: /foo/more/specific
  • prefix: /bar
  • prefix: /foo

Example setup steps

  1. Follow the guides in Forward requests to a destination to set up each route table that you want to include in this sub-table set. For each route table, include the following additional settings for delegation:

    • In the spec section, do not include the hosts, virtualGateways, or workloadSelectors fields. The parent route table dictates these fields instead.
    • Optional: If you want to refer to the sub-tables by label rather than by table name, add a label in the metadata section. Be sure to use the same label for each sub-table.
    • Example: For example, say that you are testing multiple types of request matching for myapp. You define two different route tables, one for exact and one for prefix matching, and label them as table: myapp. Your sub-tables might look like the following configurations:
      apiVersion: networking.gloo.solo.io/v2
kind: RouteTable
metadata:
  name: exact-match
  namespace: global
  # Label for the sub-table set
  labels:
    table: myapp
spec:
  http:
  # Match only requests to exactly 'one.solo.io/myapp/foo'
  - matchers:
    - uri:
        exact: /myapp/foo
    forwardTo:
      destinations:
      - ref:
          name: myapp
          namespace: global
          cluster: ${CLUSTER_NAME}
        port:
          number: 8090
        kind: SERVICE
---
apiVersion: networking.gloo.solo.io/v2
kind: RouteTable
metadata:
  name: prefix-match
  namespace: global
  # Label for the sub-table set
  labels:
    table: myapp
spec:
  http:
  # Match any requests to 'one.solo.io/myapp/.*'
  - matchers:
    - uri:
        prefix: /myapp
        ignoreCase: true
    forwardTo:
      destinations:
      - ref:
          name: myapp
          namespace: global
          cluster: ${CLUSTER_NAME}
        port:
          number: 8090
        kind: SERVICE

  2. Create the parent route table to delegate requests based on individual route specificity. In this example parent table, requests to the myapp.global.svc.cluster.local host are matched against the list of all routes in sub-tables with the table: myapp label, sorted by specificity. The request is matched to the most specific route. Note that you can also specify the sub-table names instead of the label by using the routeTables.name field.

      kubectl apply --context $REMOTE_CONTEXT1 -n global -f- <<EOF
apiVersion: networking.gloo.solo.io/v2
kind: RouteTable
metadata:
  name: delegate-specificity
  namespace: global
spec:
  hosts:
    - 'myapp.global.svc.cluster.local'
  http:
  - delegate:
      # Selects tables based on label
      routeTables:
        - labels:
            table: myapp
      # Delegates based on route specificity
      sortMethod: ROUTE_SPECIFICITY
EOF