---
title: Consuming External Web Services
description: Describes a simple scenario based on Istio's Bookinfo example.
publishdate: 2018-01-31
last_update: 2019-04-11
subtitle: Mesh-external service entries for egress HTTPS traffic
attribution: Vadim Eisenberg
keywords: [traffic-management,egress,https]
target_release: 1.1
---

In many cases, not all the parts of a microservices-based application reside in a _service mesh_. Sometimes, the
microservices-based applications use functionality provided by legacy systems that reside outside the mesh. You may want
to migrate these systems to the service mesh gradually. Until these systems are migrated, they must be accessed by the
applications inside the mesh. In other cases, the applications use web services provided by third parties.

In this blog post, I modify the [Istio Bookinfo Sample Application](/docs/examples/bookinfo/) to fetch book details from
an external web service ([Google Books APIs](https://developers.google.com/books/docs/v1/getting_started)). I show how
to enable egress HTTPS traffic in Istio by using _mesh-external service entries_. I provide two options for egress
HTTPS traffic and describe the pros and cons of each of the options.

## Initial setting

To demonstrate the scenario of consuming an external web service, I start with a Kubernetes cluster with [Istio installed](/docs/setup/getting-started/). Then I deploy
[Istio Bookinfo Sample Application](/docs/examples/bookinfo/). This application uses the _details_ microservice to fetch
book details, such as the number of pages and the publisher. The original _details_ microservice provides the book
details without consulting any external service.

The example commands in this blog post work with Istio 1.0+, with or without
[mutual TLS](/docs/concepts/security/#mutual-tls-authentication) enabled. The Bookinfo configuration files reside in the
`samples/bookinfo` directory of the Istio release archive.

Here is a copy of the end-to-end architecture of the application from the original
[Bookinfo sample application](/docs/examples/bookinfo/).

{{< image width="80%"
    link="/docs/examples/bookinfo/withistio.svg"
    caption="The Original Bookinfo Application"
    >}}

Perform the steps in the
[Deploying the application](/docs/examples/bookinfo/#deploying-the-application),
[Confirm the app is running](/docs/examples/bookinfo/#confirm-the-app-is-accessible-from-outside-the-cluster),
[Apply default destination rules](/docs/examples/bookinfo/#apply-default-destination-rules)
sections, and
[change Istio to the blocking-egress-by-default policy](/docs/tasks/traffic-management/egress/egress-control/#change-to-the-blocking-by-default-policy).

## Bookinfo with HTTPS access to a Google Books web service

Deploy a new version of the _details_ microservice, _v2_, that fetches the book details from [Google Books APIs](https://developers.google.com/books/docs/v1/getting_started). Run the following command; it sets the
`DO_NOT_ENCRYPT` environment variable of the service's container to `false`. This setting will instruct the deployed
service to use HTTPS (instead of HTTP) to access to the external service.

{{< text bash >}}
$ kubectl apply -f @samples/bookinfo/platform/kube/bookinfo-details-v2.yaml@ --dry-run -o yaml | kubectl set env --local -f - 'DO_NOT_ENCRYPT=false' -o yaml | kubectl apply -f -
{{< /text >}}

The updated architecture of the application now looks as follows:

{{< image width="80%"
    link="./bookinfo-details-v2.svg"
    caption="The Bookinfo Application with details V2"
    >}}

Note that the Google Books web service is outside the Istio service mesh, the boundary of which is marked by a dashed
line.

Now direct all the traffic destined to the _details_ microservice, to _details version v2_.

{{< text bash >}}
$ kubectl apply -f @samples/bookinfo/networking/virtual-service-details-v2.yaml@
{{< /text >}}

Note that the virtual service relies on a destination rule that you created in the [Apply default destination rules](/docs/examples/bookinfo/#apply-default-destination-rules) section.

Access the web page of the application, after
[determining the ingress IP and port](/docs/examples/bookinfo/#determine-the-ingress-ip-and-port).

Oops... Instead of the book details you have the _Error fetching product details_ message displayed:

{{< image width="80%" link="./errorFetchingBookDetails.png" caption="The Error Fetching Product Details Message" >}}

The good news is that your application did not crash. With a good microservice design, you do not have **failure
propagation**. In your case, the failing _details_ microservice does not cause the `productpage` microservice to fail.
Most of the functionality of the application is still provided, despite the failure in the _details_ microservice. You
have **graceful service degradation**: as you can see, the reviews and the ratings are displayed correctly, and the
application is still useful.

So what might have gone wrong? Ah... The answer is that I forgot to tell you to enable traffic from inside the mesh to
an external service, in this case to the Google Books web service. By default, the Istio sidecar proxies
([Envoy proxies](https://www.envoyproxy.io)) **block all the traffic to destinations outside the cluster**. To enable
such traffic, you must define a
[mesh-external service entry](/docs/reference/config/networking/service-entry/).

### Enable HTTPS access to a Google Books web service

No worries, define a **mesh-external service entry** and fix your application. You must also define a _virtual
service_ to perform routing by [SNI](https://en.wikipedia.org/wiki/Server_Name_Indication) to the external service.

{{< text bash >}}
$ kubectl apply -f - <<EOF
apiVersion: networking.istio.io/v1alpha3
kind: ServiceEntry
metadata:
  name: googleapis
spec:
  hosts:
  - www.googleapis.com
  ports:
  - number: 443
    name: https
    protocol: HTTPS
  location: MESH_EXTERNAL
  resolution: DNS
---
apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: googleapis
spec:
  hosts:
  - www.googleapis.com
  tls:
  - match:
    - port: 443
      sni_hosts:
      - www.googleapis.com
    route:
    - destination:
        host: www.googleapis.com
        port:
          number: 443
      weight: 100
EOF
{{< /text >}}

Now accessing the web page of the application displays the book details without error:

{{< image width="80%" link="./externalBookDetails.png" caption="Book Details Displayed Correctly" >}}

You can query your service entries:

{{< text bash >}}
$ kubectl get serviceentries
NAME         AGE
googleapis   8m
{{< /text >}}

You can delete your service entry:

{{< text bash >}}
$ kubectl delete serviceentry googleapis
serviceentry "googleapis" deleted
{{< /text >}}

and see in the output that the service entry is deleted.

Accessing the web page after deleting the service entry produces the same error that you experienced before, namely
_Error fetching product details_. As you can see, the service entries are defined **dynamically**, as are many other
Istio configuration artifacts. The Istio operators can decide dynamically which domains they allow the microservices to
access. They can enable and disable traffic to the external domains on the fly, without redeploying the microservices.

### Cleanup of HTTPS access to a Google Books web service

{{< text bash >}}
$ kubectl delete serviceentry googleapis
$ kubectl delete virtualservice googleapis
$ kubectl delete -f @samples/bookinfo/networking/virtual-service-details-v2.yaml@
$ kubectl delete -f @samples/bookinfo/platform/kube/bookinfo-details-v2.yaml@
{{< /text >}}

## TLS origination by Istio

There is a caveat to this story. Suppose you want to monitor which specific set of
[Google APIs](https://developers.google.com/apis-explorer/) your microservices use
([Books](https://developers.google.com/books/docs/v1/getting_started),
[Calendar](https://developers.google.com/calendar/), [Tasks](https://developers.google.com/tasks/) etc.)
Suppose you want to enforce a policy that using only
[Books APIs](https://developers.google.com/books/docs/v1/getting_started) is allowed. Suppose you want to monitor the
book identifiers that your microservices access. For these monitoring and policy tasks you need to know the URL path.
Consider for example the URL
[`www.googleapis.com/books/v1/volumes?q=isbn:0486424618`](https://www.googleapis.com/books/v1/volumes?q=isbn:0486424618).
In that URL, [Books APIs](https://developers.google.com/books/docs/v1/getting_started) is specified by the path segment
`/books`, and the [ISBN](https://en.wikipedia.org/wiki/International_Standard_Book_Number) number by the path segment
`/volumes?q=isbn:0486424618`. However, in HTTPS, all the HTTP details (hostname, path, headers etc.) are encrypted and
such monitoring and policy enforcement by the sidecar proxies is not possible. Istio can only know the server name of
the encrypted requests by the [SNI](https://tools.ietf.org/html/rfc3546#section-3.1) (_Server Name Indication_) field,
in this case `www.googleapis.com`.

To allow Istio to perform monitoring and policy enforcement of egress requests based on HTTP details, the microservices
must issue HTTP requests. Istio then opens an HTTPS connection to the destination (performs TLS origination). The code
of the microservices must be written differently or configured differently, according to whether the microservice runs
inside or outside an Istio service mesh. This contradicts the Istio design goal of [maximizing transparency](/docs/ops/deployment/architecture/#design-goals). Sometimes you need to compromise...

The diagram below shows two options for sending HTTPS traffic to external services. On the top, a microservice sends
regular HTTPS requests, encrypted end-to-end. On the bottom, the same microservice sends unencrypted HTTP requests
inside a pod, which are intercepted by the sidecar Envoy proxy. The sidecar proxy performs TLS origination, so the
traffic between the pod and the external service is encrypted.

{{< image width="60%"
    link="./https_from_the_app.svg"
    caption="HTTPS traffic to external services, with TLS originated by the microservice vs. by the sidecar proxy"
    >}}

Here is how both patterns are supported in the
[Bookinfo details microservice code]({{< github_file >}}/samples/bookinfo/src/details/details.rb), using the Ruby
[net/http module](https://docs.ruby-lang.org/en/2.0.0/Net/HTTP.html):

{{< text ruby >}}
uri = URI.parse('https://www.googleapis.com/books/v1/volumes?q=isbn:' + isbn)
http = Net::HTTP.new(uri.host, ENV['DO_NOT_ENCRYPT'] === 'true' ? 80:443)
...
unless ENV['DO_NOT_ENCRYPT'] === 'true' then
     http.use_ssl = true
end
{{< /text >}}

When the `DO_NOT_ENCRYPT` environment variable is defined, the request is performed without SSL (plain HTTP) to port 80.

You can set the `DO_NOT_ENCRYPT` environment variable to _"true"_ in the
[Kubernetes deployment spec of details v2]({{< github_file >}}/samples/bookinfo/platform/kube/bookinfo-details-v2.yaml),
the `container` section:

{{< text yaml >}}
env:
- name: DO_NOT_ENCRYPT
  value: "true"
{{< /text >}}

In the next section you will configure TLS origination for accessing an external web service.

## Bookinfo with TLS origination to a Google Books web service

1.  Deploy a version of _details v2_ that sends an HTTP request to
    [Google Books APIs](https://developers.google.com/books/docs/v1/getting_started). The `DO_NOT_ENCRYPT` variable
    is set to true in
    [`bookinfo-details-v2.yaml`]({{< github_file >}}/samples/bookinfo/platform/kube/bookinfo-details-v2.yaml).

    {{< text bash >}}
    $ kubectl apply -f @samples/bookinfo/platform/kube/bookinfo-details-v2.yaml@
    {{< /text >}}

1.  Direct the traffic destined to the _details_ microservice, to _details version v2_.

    {{< text bash >}}
    $ kubectl apply -f @samples/bookinfo/networking/virtual-service-details-v2.yaml@
    {{< /text >}}

1.  Create a mesh-external service entry for `www.google.apis` , a virtual service to rewrite the destination port from
    80 to 443, and a destination rule to perform TLS origination.

    {{< text bash >}}
    $ kubectl apply -f - <<EOF
    apiVersion: networking.istio.io/v1alpha3
    kind: ServiceEntry
    metadata:
      name: googleapis
    spec:
      hosts:
      - www.googleapis.com
      ports:
      - number: 80
        name: http
        protocol: HTTP
      - number: 443
        name: https
        protocol: HTTPS
      resolution: DNS
    ---
    apiVersion: networking.istio.io/v1alpha3
    kind: VirtualService
    metadata:
      name: rewrite-port-for-googleapis
    spec:
      hosts:
      - www.googleapis.com
      http:
      - match:
        - port: 80
        route:
        - destination:
            host: www.googleapis.com
            port:
              number: 443
    ---
    apiVersion: networking.istio.io/v1alpha3
    kind: DestinationRule
    metadata:
      name: originate-tls-for-googleapis
    spec:
      host: www.googleapis.com
      trafficPolicy:
        loadBalancer:
          simple: ROUND_ROBIN
        portLevelSettings:
        - port:
            number: 443
          tls:
            mode: SIMPLE # initiates HTTPS when accessing www.googleapis.com
    EOF
    {{< /text >}}

1.  Access the web page of the application and verify that the book details are displayed without errors.

1.  [Enable Envoy’s access logging](/docs/tasks/observability/logs/access-log/#enable-envoy-s-access-logging)

1.  Check the log of of the sidecar proxy of _details v2_ and see the HTTP request.

    {{< text bash >}}
    $ kubectl logs $(kubectl get pods -l app=details -l version=v2 -o jsonpath='{.items[0].metadata.name}') istio-proxy | grep googleapis
    [2018-08-09T11:32:58.171Z] "GET /books/v1/volumes?q=isbn:0486424618 HTTP/1.1" 200 - 0 1050 264 264 "-" "Ruby" "b993bae7-4288-9241-81a5-4cde93b2e3a6" "www.googleapis.com:80" "172.217.20.74:80"
    EOF
    {{< /text >}}

    Note the URL path in the log, the path can be monitored and access policies can be applied based on it. To read more
    about monitoring and access policies for HTTP egress traffic, check out [this blog post](https://archive.istio.io/v0.8/blog/2018/egress-monitoring-access-control/#logging).

### Cleanup of TLS origination to a Google Books web service

{{< text bash >}}
$ kubectl delete serviceentry googleapis
$ kubectl delete virtualservice rewrite-port-for-googleapis
$ kubectl delete destinationrule originate-tls-for-googleapis
$ kubectl delete -f @samples/bookinfo/networking/virtual-service-details-v2.yaml@
$ kubectl delete -f @samples/bookinfo/platform/kube/bookinfo-details-v2.yaml@
{{< /text >}}

### Relation to Istio mutual TLS

Note that the TLS origination in this case is unrelated to
[the mutual TLS](/docs/concepts/security/#mutual-tls-authentication) applied by Istio. The TLS origination for the
external services will work, whether the Istio mutual TLS is enabled or not. The **mutual** TLS secures
service-to-service communication **inside** the service mesh and provides each service with a strong identity. The
**external services** in this blog post were accessed using **one-way TLS**, the same mechanism used to secure communication between a
web browser and a web server. TLS is applied to the communication with external services to verify the identity of the
external server and to encrypt the traffic.

## Conclusion

In this blog post I demonstrated how microservices in an Istio service mesh can consume external web services by
HTTPS. By default, Istio blocks all the traffic to the hosts outside the cluster. To enable such traffic, mesh-external
service entries must be created for the service mesh. It is possible to access the external sites either by
issuing HTTPS requests, or by issuing HTTP requests with Istio performing TLS origination. When the microservices issue
HTTPS requests, the traffic is encrypted end-to-end, however Istio cannot monitor HTTP details like the URL paths of the
requests. When the microservices issue HTTP requests, Istio can monitor the HTTP details of the requests and enforce
HTTP-based access policies. However, in that case the traffic between microservice and the sidecar proxy is unencrypted.
Having part of the traffic unencrypted can be forbidden in organizations with very strict security requirements.
