Transformation
Alter a request before matching and routing, such as with an Inja header template.
You might transform the request or response to match a different routing destination based on the transformed content. You can also apply special transformations, such as via Inja templates. With Inja, you can write loops, conditional logic, and other functions to transform requests and responses.
For more information, see the following resources.
- Gloo Mesh Enterprise API docs
- The following video that shows how you might use transformation policies with other Gloo policies such as JWT and rate limiting.
Before you begin
This guide assumes that you use the same names for components like clusters, workspaces, and namespaces as in the getting started. If you have different names, make sure to update the sample configuration files in this guide.
Complete the multicluster getting started guide to set up the following testing environment.
- Three clusters along with environment variables for the clusters and their Kubernetes contexts.
- The Gloo
meshctl
CLI, along with other CLI tools such askubectl
andistioctl
. - The Gloo management server in the management cluster, and the Gloo agents in the workload clusters.
- Istio installed in the workload clusters.
- A simple Gloo workspace setup.
- Install Bookinfo and other sample apps.
Configure transformation policies
You can apply a transformation policy at the route level. For more information, see Apply policies.
When you attempt to apply multiple transformation policies, all policies are first sorted ascending by creation time, and then grouped by stage (preAuthz
and postAuthz
). For each stage, only the oldest policy is applied. All subsequent policies are ignored. Note that this behavior applies even if you specify the prioritizedPhase
field in your transformation policy.
Review the following sample configuration files.
Request transformation
The following example is to inject a header with a simple Inja template into a request.
apiVersion: trafficcontrol.policy.gloo.solo.io/v2
kind: TransformationPolicy
metadata:
annotations:
cluster.solo.io/cluster: ""
name: basic-auth
namespace: bookinfo
spec:
applyToRoutes:
- route:
labels:
route: ratings
config:
request:
injaTemplate:
headers:
foo:
text: bar
Review the following table to understand this configuration. For more information, see the API docs.
Setting | Description |
---|---|
spec.applyToRoutes | Use labels to configure which routes to apply the policy to. This example label matches the app and route from the example route table that you apply separately. If omitted and you do not have another selector such as applyToDestinations , the policy applies to all routes in the workspace. |
config.request | Transform the request before sending to the upstream service. The example adds a foo: bar header. |
Response transformation
The following example is to inject a header with a simple Inja template into a response.
apiVersion: trafficcontrol.policy.gloo.solo.io/v2
kind: TransformationPolicy
metadata:
annotations:
cluster.solo.io/cluster: ""
name: basic-auth
namespace: bookinfo
spec:
applyToRoutes:
- route:
labels:
route: ratings
config:
response:
injaTemplate:
headers:
foo:
text: bar
Review the following table to understand this configuration. For more information, see the API docs.
Setting | Description |
---|---|
spec.applyToRoutes | Use labels to configure which routes to apply the policy to. This example label matches the app and route from the example route table that you apply separately. If omitted and you do not have another selector such as applyToDestinations , the policy applies to all routes in the workspace. |
config.response | Transform the response before returning to the client. The example adds a foo: bar header. |
Replace request and response string with random
You can use a replace_with_random
function in a transformation policy to replace a string in a request and response with a random, unique value per request-response pair in the header, body, or metadata. For example, you might have a request with an ID, nonce, or other sanitized value that shares the value with other requests. You want to replace this value with a new, random value that is unique to the request so that you can build response-specific logic in your app.
- The function is in the format:
replace_with_random(source_string, pattern_to_replace_string)
. - The
pattern_to_replace_string
pattern is an exact match string. - The replaced value is a 128-bit, base64-encoded random number.
Review the following example Inja template.
apiVersion: trafficcontrol.policy.gloo.solo.io/v2
kind: TransformationPolicy
metadata:
annotations:
cluster.solo.io/cluster: ""
name: transformation-one
namespace: bookinfo
spec:
applyToRoutes:
- route:
labels:
route: ratings
config:
phase:
postAuthz:
priority: 10
response:
injaTemplate:
advancedTemplates: false
parseBodyBehavior: DontParse
headers:
baz:
text: '{{ replace_with_random(header("baz"), "pattern-to-replace") }}'
foo:
text: '{{ replace_with_random(header("x-foo"), "another-pattern-to-replace") }}'
body:
text: ' {{ replace_with_random(body(), "pattern-to-replace") }}'
Review the following table to understand this configuration. For more information, see the API docs.
Setting | Description |
---|---|
spec.applyToRoutes | Use labels to configure which routes to apply the policy to. This example label matches the app and route from the example route table that you apply separately. If omitted and you do not have another selector such as applyToDestinations , the policy applies to all routes in the workspace. |
config.phase | Set when to apply the transformation filter in the request chain, either before (preAuthz ) or after (postAuthz ) authorization. You can also set the priority if you have multiple policies in the same phase. The lowest numbered priority is run first. For more information, see Order of applied policies. This example sets postAuthz so that the policy can extract authorization information such as an external auth ID or JWT token. |
config.response.injaTemplate | The Inja template with header and body rules to use to transform data in the response that is received from the upstream service before returning the response to the client. To configure an Inja template to transform data before sending a request to an upstream, you can use config.request.injaTemplate . |
advancedTemplates: false | Set to false to use simple naming and dot notation (such as time.start ) for the extraction rules in the template. For more information, see the Envoy transformation proto. |
parseBodyBehavior: DontParse | Set to DontParse to treat the response and request bodies as plain text, not JSON (ParseAsJson ). |
headers | Configure the replacement rules for request headers. The example replaces the pattern-to-replace pattern in the baz header and the another-pattern-to-replace pattern in the x-foo header. |
body | Configure the replacement rules for the request body. The example replaces the pattern-to-replace pattern anywhere in the request body. The replacement value for the pattern-to-replace pattern in the body is the same as the replacement value in the baz header because the patterns match. However, the replacement value for the body differs from the foo header because the patterns do not match. |
Verify transformation policies
Log in to the reviews app and send a request to the
ratings
app. Make sure that a 200 HTTP response code is returned. Create a temporary curl pod in thebookinfo
namespace, so that you can test the app setup. You can also use this method in Kubernetes 1.23 or later, but an ephemeral container might be simpler.- Create the curl pod.
kubectl run -it -n bookinfo --context ${REMOTE_CONTEXT1} curl --image=curlimages/curl:7.73.0 --rm -- sh
- Send a request to the httpbin app.
curl -v http://ratings:9080/ratings/1
- Exit the temporary pod. The pod deletes itself.
exit
Example output:
< HTTP/1.1 200 OK < content-type: application/json < date: Wed, 17 May 2023 14:45:24 GMT < x-envoy-upstream-service-time: 22 < server: envoy < transfer-encoding: chunked Connection #0 to host ratings left intact {"id":1,"ratings":{"Reviewer1":5,"Reviewer2":4}}%
- Create the curl pod.
Apply a transformation policy to the ratings app that adds the
foo: bar
response header.kubectl apply --context ${REMOTE_CONTEXT1} -f- <<EOF apiVersion: trafficcontrol.policy.gloo.solo.io/v2 kind: TransformationPolicy metadata: annotations: cluster.solo.io/cluster: "" name: basic-auth namespace: bookinfo spec: applyToRoutes: - route: labels: route: ratings config: response: injaTemplate: headers: foo: text: bar EOF
Create a route table for the ratings app.
kubectl apply --context ${REMOTE_CONTEXT1} -f- <<EOF apiVersion: networking.gloo.solo.io/v2 kind: RouteTable metadata: name: ratings-rt namespace: bookinfo spec: hosts: - ratings http: - forwardTo: destinations: - ref: name: ratings namespace: bookinfo cluster: ${REMOTE_CLUSTER1} labels: route: ratings workloadSelectors: - {} EOF
Send another request to the ratings app by using the command in step 1. Verify that you now see the
foo: bar
header in your response.Example output:
< HTTP/1.1 200 OK < content-type: application/json < date: Wed, 17 May 2023 16:48:51 GMT < x-envoy-upstream-service-time: 2 < server: envoy < foo: bar < transfer-encoding: chunked * Connection #0 to host ratings left intact {"id":1,"ratings":{"Reviewer1":5,"Reviewer2":4}}%
Cleanup
You can optionally remove the resources that you set up as part of this guide.
kubectl -n bookinfo --context $REMOTE_CONTEXT1 delete transformationpolicy basic-auth
kubectl -n bookinfo --context $REMOTE_CONTEXT1 delete routetable ratings-rt