Guided Exercise: Troubleshoot Containers and Pods

Troubleshoot and fix a failed MySQL pod and manually initialize a database with test data.

Outcomes

Investigate errors with creating a pod.
View the status, logs, and events for a pod.
Copy files into a running pod.
Connect to a running pod by using port forwarding.

As the student user on the workstation machine, use the lab command to prepare your system for this exercise.

This command ensures that the cluster and all exercise resources are available.

[student@workstation ~]$ lab start pods-troubleshooting

Procedure 3.3. Instructions

 [student@workstation ~]$ oc login -u developer -p developer \
 https://api.ocp4.example.com:6443
 ...output omitted...

Create the pods-troubleshooting project.

 [student@workstation ~]$ oc new-project pods-troubleshooting
 ...output omitted...

Create a MySQL pod called mysql-server with the oc run command. Use the registry.ocp4.example.com:8443/rhel9/mysql-80:1228 container image for the pod. Specify the environment variables with the following values:

| Variable | Value | | --- | --- | | MYSQL_USER | redhat | | MYSQL_PASSWORD | redhat123 | | MYSQL_DATABASE | world |

Then, view the status of the pod with the oc get command.
1. Create the mysql-server pod with the oc run command. Specify the environment values with the --env option.
```
 [student@workstation ~]$ oc run mysql-server \
   --image registry.ocp4.example.com:8443/rhel9/mysql-80:1228 \
   --env MYSQL_USER=redhat \
   --env MYSQL_PASSWORD=redhat123 \
   --env MYSQL_DATABASE=world
 pod/mysql created
```
2. After a few moments, retrieve the status of the pod. Execute the oc get pods command a few times to view the status updates for the pod.
```
 [student@workstation ~]$ oc get pods
 NAME           READY   STATUS             RESTARTS   AGE
 mysql-server   0/1     ErrImagePull       0          30s
```
```
 [studet@workstation ~]$ oc get pods
 NAME           READY   STATUS             RESTARTS   AGE
 mysql-server   0/1     ImagePullBackoff   0          45s
```
  The pod failed to start.

Identify the root cause of the pod's failure.

Retrieve the pod's logs with the oc logs command.

 [student@workstation ~]$ oc logs mysql-server
 Error from server (BadRequest): container "mysql-server" in pod "mysql-server" is waiting to start: trying and failing to pull image

The logs state that the pod cannot pull the container image.

Retrieve the events log with the oc get events command.

 student@workstation ~]$ oc get events
 LAST SEEN   TYPE      REASON           OBJECT             MESSAGE
 33s         Normal    Scheduled        pod/mysql-server   Successfully assigned pods-troubleshooting/mysql-server to master01 by master01
 31s         Normal    AddedInterface   pod/mysql-server   Add eth0 [10.8.0.68/23] from ovn-kubernetes
 16s         Normal    Pulling          pod/mysql-server   Pulling image "registry.ocp4.example.com:8443/rhel9/mysql-80:1228"
 16s         Warning   Failed           pod/mysql-server   Failed to pull image "registry.ocp4.example.com:8443/rhel9/mysql-80:1228": rpc error: code = Unknown desc = reading manifest 1228 in registry.ocp4.example.com:8443/rhel9/mysql-80: manifest unknown: manifest unknown
 16s         Warning   Failed           pod/mysql-server   Error: ErrImagePull
 4s          Normal    BackOff          pod/mysql-server   Back-off pulling image "registry.ocp4.example.com:8443/rhel9/mysql-80:1228"
 4s          Warning   Failed           pod/mysql-server   Error: ImagePullBackOff

The output states that the image pull failed because the 1228 manifest is unknown. This failure could mean that the manifest, or image tag, does not exist in the repository.

Inspect the available manifest in the registry.ocp4.example.com:8443/rhel9/mysql-80 container repository. Authenticate to the container repository with the skopeo login command as the developer user with the developer password. Then, use the skopeo inspect command to retrieve the available manifests in the registry.ocp4.example.com:8443/rhel9/mysql-80 repository.

 [student@workstation ~]$ skopeo login registry.ocp4.example.com:8443
 Username: developer
 Password: developer
 Login Succeeded!

 [student@workstation ~]$ skopeo inspect \
   docker://registry.ocp4.example.com:8443/rhel9/mysql-80
 ...output omitted...
     "Name": "registry.ocp4.example.com:8443/rhel9/mysql-80",
     "Digest": "sha256:d282...f38f",
     "RepoTags": [
         "1-237",
         "1-228",
         "1-228-source",
         "1-224",
         "1-224-source",
         "1",
         "latest
     ],
 ...output omitted...

The 1228 manifest, or tag, is not available in the repository, which means that the registry.ocp4.example.com:8443/rhel9/mysql-80:1228 image does not exist. However, the 1-228 tag does exist.

The pod failed to start because of a typing error in the image tag. Update the pod's configuration to use the registry.ocp4.example.com:8443/rhel9/mysql-80:1-228 container image. Confirm that the pod is re-created after editing the resource.
1. Edit the pod's configuration with the oc edit command. Locate the .spec.containers.image object. Update the value to the registry.ocp4.example.com:8443/rhel9/mysql-80:1-228 container image and save the change.
```
 [student@workstation ~]$ oc edit pod/mysql-server
```
```
 ...output omitted...
 apiVersion: v1
 kind: Pod
 metadata:
 ...output omitted...
 spec:
   containers:
   - image: registry.ocp4.example.com:8443/rhel9/mysql-80:1-228
 ...output omitted...
```
2. Verify the status of the mysql-server pod with the oc get command. The pod's status might take a few moments to update after the resource edit. Repeat the oc get command until the pod's status changes.
```
 [student@workstation ~]$ oc get pods
 NAME           READY   STATUS     RESTARTS      AGE
 mysql-server   1/1     Running    0             10m
```
  The mysql-server pod successfully pulled the image and created the container. The pod now shows a Running status.

Prepare the database on the mysql-server pod. Copy the ~/DO180/labs/pods-troubleshooting/world_x.sql file to the mysql-server pod. Then, connect to the pod and execute the world_x.sql file to populate the world database.

Use the oc cp command to copy the world_x.sql file in the ~/DO180/labs/pods-troubleshooting directory to the /tmp/ directory on the mysql-server pod.
```
 [student@workstation ~]$ oc cp ~/DO180/labs/pods-troubleshooting/world_x.sql \
   mysql-server:/tmp/
```

Confirm that the world_x.sql file is accessible within the mysql-server pod with the oc exec command.

 [student@workstation ~]$ oc exec -it pod/mysql-server -- ls -la /tmp/
 total 0
 drwxrwxrwx. 1 root       root  22     Nov  4 14:45 .
 dr-xr-xr-x. 1 root       root  50     Nov  4 14:34 ..
 -rw-rw-r--. 1 1000680000 root  558791 Nov  4 14:45 world_x.sql

Connect to the mysql-server pod with the oc rsh command. Then, log in to MySQL as the redhat user with the redhat123 password.

 [student@workstation ~]$ oc rsh mysql-server

 sh-5.1$ mysql -u redhat -p
 Enter password: redhat123
 Welcome to the MySQL monitor.  Commands end with ; or \g.
 ...output omitted...
 mysql>

From the MySQL prompt, select the world database. Source the world_x.sql script inside the pod to initialize and populate the world database.
```
 mysql> USE world;
 Database changed
```
```
 mysql> SOURCE /tmp/world_x.sql;
 ...output omitted...
```

Execute the SHOW TABLES; command to confirm that the database now contains tables. Then, exit the database and the pod.

 mysql> SHOW TABLES;
 -----------------
 | Tables_in_test  |
 -----------------
 | city            |
 | country         |
 | countryinfo     |
 | countrylanguage |
 -----------------
 4 rows in set (0.00 sec)

 mysql> exit;
 Bye
 sh-5.1$ exit
 exit
 [student@workstation ~]$

Configure port forwarding and then use the MySQL client on the workstation machine to connect to the world database on the mysql-server pod. Confirm that you can access data within the world database from the workstation machine.

From the workstation machine, use the oc port-forward command to forward the 3306 local port to the 3306 port on the mysql-server pod.

 [student@workstation ~]$ oc port-forward mysql-server 3306:3306
 Forwarding from 127.0.0.1:3306 -> 3306
 Forwarding from [::1]:3306 -> 3306

Open another terminal window on the workstation machine. Connect to the world database with the local MySQL client on the workstation machine. Log in as the redhat user with the redhat123 password. Specify the host as the localhost 127.0.0.1 IP address and use 3306 as the port.
```
 [student@workstation ~]$ mysql -u redhat -p -h 127.0.0.1 -P 3306
 Enter password: redhat123
 Welcome to the MySQL monitor.  Commands end with ; or \g.
 ...output omitted...
 mysql>
```

Select the world database and execute the SHOW TABLES; command.

 mysql> USE world;
 Database changed

 mysql> SHOW TABLES;
 -----------------
 | Tables_in_test  |
 -----------------
 | city            |
 | country         |
 | countryinfo     |
 | countrylanguage |
 -----------------
 4 rows in set (0.01 sec)

Confirm that you can retrieve data from the country table. Execute the SELECT COUNT(*) FROM country command to retrieve the number of countries within the country table.
```
 mysql> SELECT COUNT(*) FROM country;
 ----------
 | COUNT(*) |
 ----------
 |      239 |
 ----------
 1 row in set (0.01 sec)
```

Exit the database.

 mysql> exit;
 Bye
 [student@workstation ~]$

Return to the terminal that is executing the oc port-forward command. Press Ctrl+C to end the connection.

 [student@workstation ~]$ oc port-forward mysql-server 3306:3306
 Forwarding from 127.0.0.1:3306 -> 3306
 Forwarding from [::1]:3306 -> 3306
 Handling connection for 3306
 Handling connection for 3306
 ^C[student@workstation ~]$

Finish

On the workstation machine, use the lab command to complete this exercise. This step is important to ensure that resources from previous exercises do not impact upcoming exercises.

[student@workstation ~]$ lab finish pods-troubleshooting

Guided Exercise: Troubleshoot Containers and Pods

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