Monitoring and Access Policies for HTTP Egress Traffic
While Istio’s main focus is management of traffic between microservices inside a service mesh, Istio can also manage ingress (from outside into the mesh) and egress (from the mesh outwards) traffic. Istio can uniformly enforce access policies and aggregate telemetry data for mesh-internal, ingress and egress traffic.
In this blog post, we show how to apply monitoring and access policies to HTTP egress traffic with Istio.
Use case
Consider an organization that runs applications that process content from cnn.com. The applications are decomposed into microservices deployed in an Istio service mesh. The applications access pages of various topics from cnn.com: edition.cnn.com/politics, edition.cnn.com/sport and edition.cnn.com/health. The organization configures Istio to allow access to edition.cnn.com and everything works fine. However, at some point in time, the organization decides to banish politics. Practically, it means blocking access to edition.cnn.com/politics and allowing access to edition.cnn.com/sport and edition.cnn.com/health only. The organization will grant permissions to individual applications and to particular users to access edition.cnn.com/politics, on a case-by-case basis.
To achieve that goal, the organization’s operations people monitor access to the external services and analyze Istio logs to verify that no unauthorized request was sent to edition.cnn.com/politics. They also configure Istio to prevent access to edition.cnn.com/politics automatically.
The organization is resolved to prevent any tampering with the new policy. It decides to put mechanisms in place that will prevent any possibility for a malicious application to access the forbidden topic.
Related tasks and examples
- The Control Egress Traffic task demonstrates how external (outside the Kubernetes cluster) HTTP and HTTPS services can be accessed by applications inside the mesh.
- The Configure an Egress Gateway example describes how to configure Istio to direct egress traffic through a dedicated gateway service called egress gateway.
- The Egress Gateway with TLS Origination example demonstrates how to allow applications to send HTTP requests to external servers that require HTTPS, while directing traffic through egress gateway.
- The Visualizing Metrics with Grafana describes the Istio Dashboard to monitor mesh traffic.
- The Basic Access Control task shows how to control access to in-mesh services.
- The Denials and White/Black Listing task shows how to configure access policies using black or white list checkers.
As opposed to the observability and security tasks above, this blog post describes Istio’s monitoring and access policies applied exclusively to the egress traffic.
Before you begin
Follow the steps in the Egress Gateway with TLS Origination example, with mutual TLS authentication enabled, without
the Cleanup step.
After completing that example, you can access edition.cnn.com/politics from an in-mesh container with curl
installed. This blog post assumes that the SOURCE_POD
environment variable contains the source pod’s name and that the container’s name is sleep
.
Configure monitoring and access policies
Since you want to accomplish your tasks in a secure way, you should direct egress traffic through egress gateway, as described in the Egress Gateway with TLS Origination task. The secure way here means that you want to prevent malicious applications from bypassing Istio monitoring and policy enforcement.
According to our scenario, the organization performed the instructions in the Before you begin section, enabled HTTP traffic to edition.cnn.com, and configured that traffic to pass through the egress gateway. The egress gateway performs TLS origination to edition.cnn.com, so the traffic leaves the mesh encrypted. At this point, the organization is ready to configure Istio to monitor and apply access policies for the traffic to edition.cnn.com.
Logging
Configure Istio to log access to *.cnn.com. You create a logentry
and two
stdio handlers
, one for logging forbidden access
(error log level) and another one for logging all access to *.cnn.com (info log level). Then you create rules
to
direct your logentry
instances to your handlers
. One rule directs access to *.cnn.com/politics to the handler for
logging forbidden access, another rule directs log entries to the handler that outputs each access to *.cnn.com as an
info log entry. To understand the Istio logentries
, rules
, and handlers
, see
Istio Adapter Model. A diagram with the involved entities and dependencies between them
appears below:
Create the
logentry
,rules
andhandlers
. Note that you specifycontext.reporter.uid
askubernetes://istio-egressgateway
in the rules to get logs from the egress gateway only.$ cat <<EOF | kubectl apply -f - # Log entry for egress access apiVersion: "config.istio.io/v1alpha2" kind: logentry metadata: name: egress-access namespace: istio-system spec: severity: '"info"' timestamp: request.time variables: destination: request.host | "unknown" path: request.path | "unknown" responseCode: response.code | 0 responseSize: response.size | 0 reporterUID: context.reporter.uid | "unknown" sourcePrincipal: source.principal | "unknown" monitored_resource_type: '"UNSPECIFIED"' --- # Handler for error egress access entries apiVersion: "config.istio.io/v1alpha2" kind: stdio metadata: name: egress-error-logger namespace: istio-system spec: severity_levels: info: 2 # output log level as error outputAsJson: true --- # Rule to handle access to *.cnn.com/politics apiVersion: "config.istio.io/v1alpha2" kind: rule metadata: name: handle-politics namespace: istio-system spec: match: request.host.endsWith("cnn.com") && request.path.startsWith("/politics") && context.reporter.uid.startsWith("kubernetes://istio-egressgateway") actions: - handler: egress-error-logger.stdio instances: - egress-access.logentry --- # Handler for info egress access entries apiVersion: "config.istio.io/v1alpha2" kind: stdio metadata: name: egress-access-logger namespace: istio-system spec: severity_levels: info: 0 # output log level as info outputAsJson: true --- # Rule to handle access to *.cnn.com apiVersion: "config.istio.io/v1alpha2" kind: rule metadata: name: handle-cnn-access namespace: istio-system spec: match: request.host.endsWith(".cnn.com") && context.reporter.uid.startsWith("kubernetes://istio-egressgateway") actions: - handler: egress-access-logger.stdio instances: - egress-access.logentry EOF
Send three HTTP requests to cnn.com, to edition.cnn.com/politics, edition.cnn.com/sport and edition.cnn.com/health. All three should return 200 OK.
$ kubectl exec -it $SOURCE_POD -c sleep -- sh -c 'curl -sL -o /dev/null -w "%{http_code}\n" http://edition.cnn.com/politics; curl -sL -o /dev/null -w "%{http_code}\n" http://edition.cnn.com/sport; curl -sL -o /dev/null -w "%{http_code}\n" http://edition.cnn.com/health' 200 200 200
Query the Mixer log and see that the information about the requests appears in the log:
$ kubectl -n istio-system logs -l istio-mixer-type=telemetry -c mixer | grep egress-access | grep cnn | tail -4 {"level":"info","time":"2019-01-29T07:43:24.611462Z","instance":"egress-access.logentry.istio-system","destination":"edition.cnn.com","path":"/politics","reporterUID":"kubernetes://istio-egressgateway-747b6764b8-44rrh.istio-system","responseCode":200,"responseSize":1883355,"sourcePrincipal":"cluster.local/ns/default/sa/sleep"} {"level":"info","time":"2019-01-29T07:43:24.886316Z","instance":"egress-access.logentry.istio-system","destination":"edition.cnn.com","path":"/sport","reporterUID":"kubernetes://istio-egressgateway-747b6764b8-44rrh.istio-system","responseCode":200,"responseSize":2094561,"sourcePrincipal":"cluster.local/ns/default/sa/sleep"} {"level":"info","time":"2019-01-29T07:43:25.369663Z","instance":"egress-access.logentry.istio-system","destination":"edition.cnn.com","path":"/health","reporterUID":"kubernetes://istio-egressgateway-747b6764b8-44rrh.istio-system","responseCode":200,"responseSize":2157009,"sourcePrincipal":"cluster.local/ns/default/sa/sleep"} {"level":"error","time":"2019-01-29T07:43:24.611462Z","instance":"egress-access.logentry.istio-system","destination":"edition.cnn.com","path":"/politics","reporterUID":"kubernetes://istio-egressgateway-747b6764b8-44rrh.istio-system","responseCode":200,"responseSize":1883355,"sourcePrincipal":"cluster.local/ns/default/sa/sleep"}
You see four log entries related to your three requests. Three info entries about the access to edition.cnn.com and one error entry about the access to edition.cnn.com/politics. The service mesh operators can see all the access instances, and can also search the log for error log entries that represent forbidden accesses. This is the first security measure the organization can apply before blocking the forbidden accesses automatically, namely logging all the forbidden access instances as errors. In some settings this can be a sufficient security measure.
Note the attributes:
destination
,path
,responseCode
,responseSize
are related to HTTP parameters of the requestssourcePrincipal
:cluster.local/ns/default/sa/sleep
- a string that represents thesleep
service account in thedefault
namespacereporterUID
:kubernetes://istio-egressgateway-747b6764b8-44rrh.istio-system
- a UID of the reporting pod, in this caseistio-egressgateway-747b6764b8-44rrh
in theistio-system
namespace
Access control by routing
After enabling logging of access to edition.cnn.com, automatically enforce an access policy, namely allow accessing /health and /sport URL paths only. Such a simple policy control can be implemented with Istio routing.
Redefine your
VirtualService
for edition.cnn.com:$ cat <<EOF | kubectl apply -f - apiVersion: networking.istio.io/v1alpha3 kind: VirtualService metadata: name: direct-cnn-through-egress-gateway spec: hosts: - edition.cnn.com gateways: - istio-egressgateway - mesh http: - match: - gateways: - mesh port: 80 route: - destination: host: istio-egressgateway.istio-system.svc.cluster.local subset: cnn port: number: 443 weight: 100 - match: - gateways: - istio-egressgateway port: 443 uri: regex: "/health|/sport" route: - destination: host: edition.cnn.com port: number: 443 weight: 100 EOF
Note that you added a
match
byuri
condition that checks that the URL path is either /health or /sport. Also note that this condition is added to theistio-egressgateway
section of theVirtualService
, since the egress gateway is a hardened component in terms of security (see egress gateway security considerations). You don’t want any tampering with your policies.Send the previous three HTTP requests to cnn.com:
$ kubectl exec -it $SOURCE_POD -c sleep -- sh -c 'curl -sL -o /dev/null -w "%{http_code}\n" http://edition.cnn.com/politics; curl -sL -o /dev/null -w "%{http_code}\n" http://edition.cnn.com/sport; curl -sL -o /dev/null -w "%{http_code}\n" http://edition.cnn.com/health' 404 200 200
The request to edition.cnn.com/politics returned 404 Not Found, while requests to edition.cnn.com/sport and edition.cnn.com/health returned 200 OK, as expected.
Query the Mixer log and see that the information about the requests appears again in the log:
$ kubectl -n istio-system logs -l istio-mixer-type=telemetry -c mixer | grep egress-access | grep cnn | tail -4 {"level":"info","time":"2019-01-29T07:55:59.686082Z","instance":"egress-access.logentry.istio-system","destination":"edition.cnn.com","path":"/politics","reporterUID":"kubernetes://istio-egressgateway-747b6764b8-44rrh.istio-system","responseCode":404,"responseSize":0,"sourcePrincipal":"cluster.local/ns/default/sa/sleep"} {"level":"info","time":"2019-01-29T07:55:59.697565Z","instance":"egress-access.logentry.istio-system","destination":"edition.cnn.com","path":"/sport","reporterUID":"kubernetes://istio-egressgateway-747b6764b8-44rrh.istio-system","responseCode":200,"responseSize":2094561,"sourcePrincipal":"cluster.local/ns/default/sa/sleep"} {"level":"info","time":"2019-01-29T07:56:00.264498Z","instance":"egress-access.logentry.istio-system","destination":"edition.cnn.com","path":"/health","reporterUID":"kubernetes://istio-egressgateway-747b6764b8-44rrh.istio-system","responseCode":200,"responseSize":2157009,"sourcePrincipal":"cluster.local/ns/default/sa/sleep"} {"level":"error","time":"2019-01-29T07:55:59.686082Z","instance":"egress-access.logentry.istio-system","destination":"edition.cnn.com","path":"/politics","reporterUID":"kubernetes://istio-egressgateway-747b6764b8-44rrh.istio-system","responseCode":404,"responseSize":0,"sourcePrincipal":"cluster.local/ns/default/sa/sleep"}
You still get info and error messages regarding accesses to edition.cnn.com/politics, however this time the
responseCode
is404
, as expected.
While implementing access control using Istio routing worked for us in this simple case, it would not suffice for more complex cases. For example, the organization may want to allow access to edition.cnn.com/politics under certain conditions, so more complex policy logic than just filtering by URL paths will be required. You may want to apply Istio Mixer Adapters, for example white lists or black lists of allowed/forbidden URL paths, respectively. Policy Rules allow specifying complex conditions, specified in a rich expression language, which includes AND and OR logical operators. The rules can be reused for both logging and policy checks. More advanced users may want to apply Istio Role-Based Access Control.
An additional aspect is integration with remote access policy systems. If the organization in our use case operates some Identity and Access Management system, you may want to configure Istio to use access policy information from such a system. You implement this integration by applying Istio Mixer Adapters.
Cancel the access control by routing you used in this section and implement access control by Mixer policy checks in the next section.
Replace the
VirtualService
for edition.cnn.com with your previous version from the Configure an Egress Gateway example:$ cat <<EOF | kubectl apply -f - apiVersion: networking.istio.io/v1alpha3 kind: VirtualService metadata: name: direct-cnn-through-egress-gateway spec: hosts: - edition.cnn.com gateways: - istio-egressgateway - mesh http: - match: - gateways: - mesh port: 80 route: - destination: host: istio-egressgateway.istio-system.svc.cluster.local subset: cnn port: number: 443 weight: 100 - match: - gateways: - istio-egressgateway port: 443 route: - destination: host: edition.cnn.com port: number: 443 weight: 100 EOF
Send the previous three HTTP requests to cnn.com, this time you should get three 200 OK responses as previously:
$ kubectl exec -it $SOURCE_POD -c sleep -- sh -c 'curl -sL -o /dev/null -w "%{http_code}\n" http://edition.cnn.com/politics; curl -sL -o /dev/null -w "%{http_code}\n" http://edition.cnn.com/sport; curl -sL -o /dev/null -w "%{http_code}\n" http://edition.cnn.com/health' 200 200 200
Access control by Mixer policy checks
In this step you use a Mixer
Listchecker
adapter, its whitelist
variety. You define a listentry
with the URL path of the request and a listchecker
to check the listentry
using a
static list of allowed URL paths, specified by the overrides
field. For an external Identity and Access Management system, use the providerurl
field instead. The updated
diagram of the instances, rules and handlers appears below. Note that you reuse the same policy rule, handle-cnn-access
both for logging and for access policy checks.
Define
path-checker
andrequest-path
:$ cat <<EOF | kubectl create -f - apiVersion: "config.istio.io/v1alpha2" kind: listchecker metadata: name: path-checker namespace: istio-system spec: overrides: ["/health", "/sport"] # overrides provide a static list blacklist: false --- apiVersion: "config.istio.io/v1alpha2" kind: listentry metadata: name: request-path namespace: istio-system spec: value: request.path EOF
Modify the
handle-cnn-access
policy rule to sendrequest-path
instances to thepath-checker
:$ cat <<EOF | kubectl apply -f - # Rule handle egress access to cnn.com apiVersion: "config.istio.io/v1alpha2" kind: rule metadata: name: handle-cnn-access namespace: istio-system spec: match: request.host.endsWith(".cnn.com") && context.reporter.uid.startsWith("kubernetes://istio-egressgateway") actions: - handler: egress-access-logger.stdio instances: - egress-access.logentry - handler: path-checker.listchecker instances: - request-path.listentry EOF
Perform your usual test by sending HTTP requests to edition.cnn.com/politics, edition.cnn.com/sport and edition.cnn.com/health. As expected, the request to edition.cnn.com/politics returns 403 (Forbidden).
$ kubectl exec -it $SOURCE_POD -c sleep -- sh -c 'curl -sL -o /dev/null -w "%{http_code}\n" http://edition.cnn.com/politics; curl -sL -o /dev/null -w "%{http_code}\n" http://edition.cnn.com/sport; curl -sL -o /dev/null -w "%{http_code}\n" http://edition.cnn.com/health' 403 200 200
Access control by Mixer policy checks, part 2
After the organization in our use case managed to configure logging and access control, it decided to extend its access policy by allowing the applications with a special Service Account to access any topic of cnn.com, without being monitored. You’ll see how this requirement can be configured in Istio.
Start the sleep sample with the
politics
service account.$ sed 's/: sleep/: politics/g' @samples/sleep/sleep.yaml@ | kubectl create -f - serviceaccount "politics" created service "politics" created deployment "politics" created
Define the
SOURCE_POD_POLITICS
shell variable to hold the name of the source pod with thepolitics
service account, for sending requests to external services.$ export SOURCE_POD_POLITICS=$(kubectl get pod -l app=politics -o jsonpath={.items..metadata.name})
Perform your usual test of sending three HTTP requests this time from
SOURCE_POD_POLITICS
. The request to edition.cnn.com/politics returns 403, since you did not configure the exception for the politics namespace.$ kubectl exec -it $SOURCE_POD_POLITICS -c politics -- sh -c 'curl -sL -o /dev/null -w "%{http_code}\n" http://edition.cnn.com/politics; curl -sL -o /dev/null -w "%{http_code}\n" http://edition.cnn.com/sport; curl -sL -o /dev/null -w "%{http_code}\n" http://edition.cnn.com/health' 403 200 200
Query the Mixer log and see that the information about the requests from the politics namespace appears in the log:
$ kubectl -n istio-system logs -l istio-mixer-type=telemetry -c mixer | grep egress-access | grep cnn | tail -4 {"level":"info","time":"2019-01-29T08:04:42.559812Z","instance":"egress-access.logentry.istio-system","destination":"edition.cnn.com","path":"/politics","reporterUID":"kubernetes://istio-egressgateway-747b6764b8-44rrh.istio-system","responseCode":403,"responseSize":84,"sourcePrincipal":"cluster.local/ns/default/sa/politics"} {"level":"info","time":"2019-01-29T08:04:42.568424Z","instance":"egress-access.logentry.istio-system","destination":"edition.cnn.com","path":"/sport","reporterUID":"kubernetes://istio-egressgateway-747b6764b8-44rrh.istio-system","responseCode":200,"responseSize":2094561,"sourcePrincipal":"cluster.local/ns/default/sa/politics"} {"level":"error","time":"2019-01-29T08:04:42.559812Z","instance":"egress-access.logentry.istio-system","destination":"edition.cnn.com","path":"/politics","reporterUID":"kubernetes://istio-egressgateway-747b6764b8-44rrh.istio-system","responseCode":403,"responseSize":84,"sourcePrincipal":"cluster.local/ns/default/sa/politics"} {"level":"info","time":"2019-01-29T08:04:42.615641Z","instance":"egress-access.logentry.istio-system","destination":"edition.cnn.com","path":"/health","reporterUID":"kubernetes://istio-egressgateway-747b6764b8-44rrh.istio-system","responseCode":200,"responseSize":2157009,"sourcePrincipal":"cluster.local/ns/default/sa/politics"}
Note that
sourcePrincipal
iscluster.local/ns/default/sa/politics
which represents thepolitics
service account in thedefault
namespace.Redefine
handle-cnn-access
andhandle-politics
policy rules, to make the applications in the politics namespace exempt from monitoring and policy enforcement.$ cat <<EOF | kubectl apply -f - # Rule to handle access to *.cnn.com/politics apiVersion: "config.istio.io/v1alpha2" kind: rule metadata: name: handle-politics namespace: istio-system spec: match: request.host.endsWith("cnn.com") && context.reporter.uid.startsWith("kubernetes://istio-egressgateway") && request.path.startsWith("/politics") && source.principal != "cluster.local/ns/default/sa/politics" actions: - handler: egress-error-logger.stdio instances: - egress-access.logentry --- # Rule handle egress access to cnn.com apiVersion: "config.istio.io/v1alpha2" kind: rule metadata: name: handle-cnn-access namespace: istio-system spec: match: request.host.endsWith(".cnn.com") && context.reporter.uid.startsWith("kubernetes://istio-egressgateway") && source.principal != "cluster.local/ns/default/sa/politics" actions: - handler: egress-access-logger.stdio instances: - egress-access.logentry - handler: path-checker.listchecker instances: - request-path.listentry EOF
Perform your usual test from
SOURCE_POD
:$ kubectl exec -it $SOURCE_POD -c sleep -- sh -c 'curl -sL -o /dev/null -w "%{http_code}\n" http://edition.cnn.com/politics; curl -sL -o /dev/null -w "%{http_code}\n" http://edition.cnn.com/sport; curl -sL -o /dev/null -w "%{http_code}\n" http://edition.cnn.com/health' 403 200 200
Since
SOURCE_POD
does not havepolitics
service account, access to edition.cnn.com/politics is forbidden, as previously.Perform the previous test from
SOURCE_POD_POLITICS
:$ kubectl exec -it $SOURCE_POD_POLITICS -c politics -- sh -c 'curl -sL -o /dev/null -w "%{http_code}\n" http://edition.cnn.com/politics; curl -sL -o /dev/null -w "%{http_code}\n" http://edition.cnn.com/sport; curl -sL -o /dev/null -w "%{http_code}\n" http://edition.cnn.com/health' 200 200 200
Access to all the topics of edition.cnn.com is allowed.
Examine the Mixer log and see that no more requests with
sourcePrincipal
equalcluster.local/ns/default/sa/politics
appear in the log.$ kubectl -n istio-system logs -l istio-mixer-type=telemetry -c mixer | grep egress-access | grep cnn | tail -4
Comparison with HTTPS egress traffic control
In this use case the applications use HTTP and Istio Egress Gateway performs TLS origination for them. Alternatively, the applications could originate TLS themselves by issuing HTTPS requests to edition.cnn.com. In this section we describe both approaches and their pros and cons.
In the HTTP approach, the requests are sent unencrypted on the local host, intercepted by the Istio sidecar proxy and forwarded to the egress gateway. Since you configure Istio to use mutual TLS between the sidecar proxy and the egress gateway, the traffic leaves the pod encrypted. The egress gateway decrypts the traffic, inspects the URL path, the HTTP method and headers, reports telemetry and performs policy checks. If the request is not blocked by some policy check, the egress gateway performs TLS origination to the external destination (cnn.com in our case), so the request is encrypted again and sent encrypted to the external destination. The diagram below demonstrates the network flow of this approach. The HTTP protocol inside the gateway designates the protocol as seen by the gateway after decryption.
The drawback of this approach is that the requests are sent unencrypted inside the pod, which may be against security policies in some organizations. Also some SDKs have external service URLs hard-coded, including the protocol, so sending HTTP requests could be impossible. The advantage of this approach is the ability to inspect HTTP methods, headers and URL paths, and to apply policies based on them.
In the HTTPS approach, the requests are encrypted end-to-end, from the application to the external destination. The diagram below demonstrates the network flow of this approach. The HTTPS protocol inside the gateway designates the protocol as seen by the gateway.
The end-to-end HTTPS is considered a better approach from the security point of view. However, since the traffic is encrypted the Istio proxies and the egress gateway can only see the source and destination IPs and the SNI of the destination. Since you configure Istio to use mutual TLS between the sidecar proxy and the egress gateway, the identity of the source is also known. The gateway is unable to inspect the URL path, the HTTP method and the headers of the requests, so no monitoring and policies based on the HTTP information can be possible. In our use case, the organization would be able to allow access to edition.cnn.com and to specify which applications are allowed to access edition.cnn.com. However, it will not be possible to allow or block access to specific URL paths of edition.cnn.com. Neither blocking access to edition.cnn.com/politics nor monitoring such access are possible with the HTTPS approach.
We guess that each organization will consider the pros and cons of the two approaches and choose the one most appropriate to its needs.
Summary
In this blog post we showed how different monitoring and policy mechanisms of Istio can be applied to HTTP egress
traffic. Monitoring can be implemented by configuring a logging adapter. Access
policies can be implemented by configuring VirtualServices
or by configuring various policy check adapters. We
demonstrated a simple policy that allowed certain URL paths only. We also showed a more complex policy that extended the
simple policy by making an exemption to the applications with a certain service account. Finally, we compared
HTTP-with-TLS-origination egress traffic with HTTPS egress traffic, in terms of control possibilities by Istio.
Cleanup
Perform the instructions in Cleanup section of the Configure an Egress Gateway example.
Delete the logging and policy checks configuration:
$ kubectl delete logentry egress-access -n istio-system $ kubectl delete stdio egress-error-logger -n istio-system $ kubectl delete stdio egress-access-logger -n istio-system $ kubectl delete rule handle-politics -n istio-system $ kubectl delete rule handle-cnn-access -n istio-system $ kubectl delete -n istio-system listchecker path-checker $ kubectl delete -n istio-system listentry request-path
Delete the politics source pod:
$ sed 's/: sleep/: politics/g' @samples/sleep/sleep.yaml@ | kubectl delete -f - serviceaccount "politics" deleted service "politics" deleted deployment "politics" deleted