Consuming External TCP Services
Describes a simple scenario based on Istio's Bookinfo example.
In my previous blog post, Consuming External Web Services, I described how external services can be consumed by in-mesh Istio applications via HTTPS. In this post, I demonstrate consuming external services over TCP. You will use the Istio Bookinfo sample application, the version in which the book ratings data is persisted in a MySQL database. You deploy this database outside the cluster and configure the ratings microservice to use it. You define a Service Entry to allow the in-mesh applications to access the external database.
Bookinfo sample application with external ratings database
First, you set up a MySQL database instance to hold book ratings data outside of your Kubernetes cluster. Then you modify the Bookinfo sample application to use your database.
Setting up the database for ratings data
$ export MYSQL_DB_HOST=<your MySQL database host> $ export MYSQL_DB_PORT=<your MySQL database port>
In case of a local MySQL database with the default port, the values are
To initialize the database, run the following command entering the password when prompted. The command is performed with the credentials of the
adminuser, created by default by Compose for MySQL.
$ curl -s https://raw.githubusercontent.com/istio/istio/release-1.17/samples/bookinfo/src/mysql/mysqldb-init.sql | mysqlsh --sql --ssl-mode=REQUIRED -u admin -p --host $MYSQL_DB_HOST --port $MYSQL_DB_PORT
When using the
mysqlclient and a local MySQL database, run:
$ curl -s https://raw.githubusercontent.com/istio/istio/release-1.17/samples/bookinfo/src/mysql/mysqldb-init.sql | mysql -u root -p --host $MYSQL_DB_HOST --port $MYSQL_DB_PORT
Create a user with the name
bookinfoand grant it SELECT privilege on the
$ mysqlsh --sql --ssl-mode=REQUIRED -u admin -p --host $MYSQL_DB_HOST --port $MYSQL_DB_PORT -e "CREATE USER 'bookinfo' IDENTIFIED BY '<password you choose>'; GRANT SELECT ON test.ratings to 'bookinfo';"
mysqland the local database, the command is:
$ mysql -u root -p --host $MYSQL_DB_HOST --port $MYSQL_DB_PORT -e "CREATE USER 'bookinfo' IDENTIFIED BY '<password you choose>'; GRANT SELECT ON test.ratings to 'bookinfo';"
Here you apply the principle of least privilege. This means that you do not use your
adminuser in the Bookinfo application. Instead, you create a special user for the Bookinfo application ,
bookinfo, with minimal privileges. In this case, the bookinfo user only has the
SELECTprivilege on a single table.
After running the command to create the user, you may want to clean your bash history by checking the number of the last command and running
history -d <the number of the command that created the user>. You don’t want the password of the new user to be stored in the bash history. If you’re using
mysql, remove the last command from
~/.mysql_historyfile as well. Read more about password protection of the newly created user in MySQL documentation.
Inspect the created ratings to see that everything worked as expected:
$ mysqlsh --sql --ssl-mode=REQUIRED -u bookinfo -p --host $MYSQL_DB_HOST --port $MYSQL_DB_PORT -e "select * from test.ratings;" Enter password: +----------+--------+ | ReviewID | Rating | +----------+--------+ | 1 | 5 | | 2 | 4 | +----------+--------+
mysqland the local database:
$ mysql -u bookinfo -p --host $MYSQL_DB_HOST --port $MYSQL_DB_PORT -e "select * from test.ratings;" Enter password: +----------+--------+ | ReviewID | Rating | +----------+--------+ | 1 | 5 | | 2 | 4 | +----------+--------+
Set the ratings temporarily to
1to provide a visual clue when our database is used by the Bookinfo ratings service:
$ mysqlsh --sql --ssl-mode=REQUIRED -u admin -p --host $MYSQL_DB_HOST --port $MYSQL_DB_PORT -e "update test.ratings set rating=1; select * from test.ratings;" Enter password: Rows matched: 2 Changed: 2 Warnings: 0 +----------+--------+ | ReviewID | Rating | +----------+--------+ | 1 | 1 | | 2 | 1 | +----------+--------+
mysqland the local database:
$ mysql -u root -p --host $MYSQL_DB_HOST --port $MYSQL_DB_PORT -e "update test.ratings set rating=1; select * from test.ratings;" Enter password: +----------+--------+ | ReviewID | Rating | +----------+--------+ | 1 | 1 | | 2 | 1 | +----------+--------+
You used the
rootfor the local database) in the last command since the
bookinfouser does not have the
UPDATEprivilege on the
Now you are ready to deploy a version of the Bookinfo application that will use your database.
Initial setting of Bookinfo application
To demonstrate the scenario of using an external database, you start with a Kubernetes cluster with Istio installed. Then you deploy the Istio Bookinfo sample application, apply the default destination rules, and change Istio to the blocking-egress-by-default policy.
This application uses the
ratings microservice to fetch
book ratings, a number between 1 and 5. The ratings are displayed as stars for each review. There are several versions
ratings microservice. Some use MongoDB, others use MySQL
as their database.
The example commands in this blog post work with Istio 0.8+, with or without mutual TLS enabled.
As a reminder, here is the end-to-end architecture of the application from the Bookinfo sample application.
Use the database for ratings data in Bookinfo application
Modify the deployment spec of a version of the ratings microservice that uses a MySQL database, to use your database instance. The spec is in
samples/bookinfo/platform/kube/bookinfo-ratings-v2-mysql.yamlof an Istio release archive. Edit the following lines:
- name: MYSQL_DB_HOST value: mysqldb - name: MYSQL_DB_PORT value: "3306" - name: MYSQL_DB_USER value: root - name: MYSQL_DB_PASSWORD value: password
Replace the values in the snippet above, specifying the database host, port, user, and password. Note that the correct way to work with passwords in container’s environment variables in Kubernetes is to use secrets. For this example task only, you may want to write the password directly in the deployment spec. Do not do it in a real environment! I also assume everyone realizes that
"password"should not be used as a password…
Apply the modified spec to deploy the version of the ratings microservice, v2-mysql, that will use your database.
$ kubectl apply -f @samples/bookinfo/platform/kube/bookinfo-ratings-v2-mysql.yaml@ deployment "ratings-v2-mysql" created
Route all the traffic destined to the reviews service to its v3 version. You do this to ensure that the reviews service always calls the ratings service. In addition, route all the traffic destined to the ratings service to ratings v2-mysql that uses your database.
Specify the routing for both services above by adding two virtual services. These virtual services are specified in
samples/bookinfo/networking/virtual-service-ratings-mysql.yamlof an Istio release archive. Important: make sure you applied the default destination rules before running the following command.
$ kubectl apply -f @samples/bookinfo/networking/virtual-service-ratings-mysql.yaml@
The updated architecture appears below. Note that the blue arrows inside the mesh mark the traffic configured according to the virtual services we added. According to the virtual services, the traffic is sent to reviews v3 and ratings v2-mysql.
Note that the MySQL database is outside the Istio service mesh, or more precisely outside the Kubernetes cluster. The boundary of the service mesh is marked by a dashed line.
Access the webpage
Access the webpage of the application, after determining the ingress IP and port.
You have a problem… Instead of the rating stars, the message “Ratings service is currently unavailable” is currently displayed below each review:
As in Consuming External Web Services, you experience graceful service degradation, which is good. The application did not crash due to the error in the ratings microservice. The webpage of the application correctly displayed the book information, the details, and the reviews, just without the rating stars.
You have the same problem as in Consuming External Web Services, namely all the traffic outside the Kubernetes cluster, both TCP and HTTP, is blocked by default by the sidecar proxies. To enable such traffic for TCP, a mesh-external service entry for TCP must be defined.
Mesh-external service entry for an external MySQL instance
TCP mesh-external service entries come to our rescue.
Get the IP address of your MySQL database instance. As an option, you can use the host command:
$ export MYSQL_DB_IP=$(host $MYSQL_DB_HOST | grep " has address " | cut -d" " -f4)
For a local database, set
MYSQL_DB_IPto contain the IP of your machine, accessible from your cluster.
Define a TCP mesh-external service entry:
$ kubectl apply -f - <<EOF apiVersion: networking.istio.io/v1alpha3 kind: ServiceEntry metadata: name: mysql-external spec: hosts: - $MYSQL_DB_HOST addresses: - $MYSQL_DB_IP/32 ports: - name: tcp number: $MYSQL_DB_PORT protocol: tcp location: MESH_EXTERNAL EOF
Review the service entry you just created and check that it contains the correct values:
$ kubectl get serviceentry mysql-external -o yaml apiVersion: networking.istio.io/v1alpha3 kind: ServiceEntry metadata: ...
Note that for a TCP service entry, you specify
tcp as the protocol of a port of the entry. Also note that you have to
specify the IP of the external service in the list of addresses, as a CIDR block
I will talk more about TCP service entries below. For now, verify that the service entry we added fixed the problem. Access the webpage and see if the stars are back.
It worked! Accessing the web page of the application displays the ratings without error:
Note that you see a one-star rating for both displayed reviews, as expected. You changed the ratings to be one star to provide us with a visual clue that our external database is indeed being used.
As with service entries for HTTP/HTTPS, you can delete and create service entries for TCP using
Motivation for egress TCP traffic control
Some in-mesh Istio applications must access external services, for example legacy systems. In many cases, the access is not performed over HTTP or HTTPS protocols. Other TCP protocols are used, such as database-specific protocols like MongoDB Wire Protocol and MySQL Client/Server Protocol to communicate with external databases.
Next let me provide more details about the service entries for TCP traffic.
Service entries for TCP traffic
The service entries for enabling TCP traffic to a specific port must specify
TCP as the protocol of the port.
Additionally, for the MongoDB Wire Protocol, the
protocol can be specified as
MONGO, instead of
addresses field of the entry, a block of IPs in CIDR
notation must be used. Note that the
hosts field is ignored for TCP service entries.
To enable TCP traffic to an external service by its hostname, all the IPs of the hostname must be specified. Each IP must be specified by a CIDR block.
Note that all the IPs of an external service are not always known. To enable egress TCP traffic, only the IPs that are used by the applications must be specified.
Also note that the IPs of an external service are not always static, for example in the case of CDNs. Sometimes the IPs are static most of the time, but can be changed from time to time, for example due to infrastructure changes. In these cases, if the range of the possible IPs is known, you should specify the range by CIDR blocks. If the range of the possible IPs is not known, service entries for TCP cannot be used and the external services must be called directly, bypassing the sidecar proxies.
Relation to virtual machines support
Note that the scenario described in this post is different from the
Bookinfo with Virtual Machines example. In that scenario, a MySQL instance runs on an
(outside the cluster) machine (a bare metal or a VM), integrated with the Istio service mesh. The MySQL service becomes
a first-class citizen of the mesh with all the beneficial features of Istio applicable. Among other things, the service
becomes addressable by a local cluster domain name, for example by
mysqldb.vm.svc.cluster.local, and the communication
to it can be secured by
mutual TLS authentication. There is no need to create a service
entry to access this service; however, the service must be registered with Istio. To enable such integration, Istio
components (Envoy proxy, node-agent,
_istio-agent_) must be installed on the machine and the Istio control plane
(Pilot, Mixer, Citadel) must be accessible from it. See the
Istio VM-related tasks for more details.
In our case, the MySQL instance can run on any machine or can be provisioned as a service by a cloud provider. There is no requirement to integrate the machine with Istio. The Istio control plane does not have to be accessible from the machine. In the case of MySQL as a service, the machine which MySQL runs on may be not accessible and installing on it the required components may be impossible. In our case, the MySQL instance is addressable by its global domain name, which could be beneficial if the consuming applications expect to use that domain name. This is especially relevant when that expected domain name cannot be changed in the deployment configuration of the consuming applications.
testdatabase and the
$ mysqlsh --sql --ssl-mode=REQUIRED -u admin -p --host $MYSQL_DB_HOST --port $MYSQL_DB_PORT -e "drop database test; drop user bookinfo;"
mysqland the local database:
$ mysql -u root -p --host $MYSQL_DB_HOST --port $MYSQL_DB_PORT -e "drop database test; drop user bookinfo;"
Remove the virtual services:
$ kubectl delete -f @samples/bookinfo/networking/virtual-service-ratings-mysql.yaml@ Deleted config: virtual-service/default/reviews Deleted config: virtual-service/default/ratings
Undeploy ratings v2-mysql:
$ kubectl delete -f @samples/bookinfo/platform/kube/bookinfo-ratings-v2-mysql.yaml@ deployment "ratings-v2-mysql" deleted
Delete the service entry:
$ kubectl delete serviceentry mysql-external -n default Deleted config: serviceentry mysql-external
In this blog post, I demonstrated how the microservices in an Istio service mesh can consume external services via TCP. By default, Istio blocks all the traffic, TCP and HTTP, to the hosts outside the cluster. To enable such traffic for TCP, TCP mesh-external service entries must be created for the service mesh.