Environment health checks | Day Two Operations Guide | OpenShift Container Platform 3.7

Checking complete environment health
Creating alerts using Prometheus
Host health
Router and registry health
Network connectivity
- Connectivity on master hosts
- Connectivity on node instances
Storage
Docker storage
API service status
Controller role verification
Verifying correct Maximum Transmission Unit (MTU) size

This topic contains steps to verify the overall health of the OpenShift Container Platform cluster and the various components, as well as describing the intended behavior.

Knowing the verification process for the various components is the first step to troubleshooting issues. If experiencing issues, you can use the checks provided in this section to diagnose any problems.

Checking complete environment health

To verify the end-to-end functionality of an OpenShift Container Platform cluster, build and deploy an example application.

Procedure

Create a new project named validate, as well as an example application from the cakephp-mysql-example template:
```
$ oc new-project validate
$ oc new-app cakephp-mysql-example
```
You can check the logs to follow the build:
```
$ oc logs -f bc/cakephp-mysql-example
```

Once the build is complete, two pods should be running: a database and an application:

$ oc get pods
NAME                            READY     STATUS      RESTARTS   AGE
cakephp-mysql-example-1-build   0/1       Completed   0          1m
cakephp-mysql-example-2-247xm   1/1       Running     0          39s
mysql-1-hbk46                   1/1       Running     0          1m

Visit the application URL. The Cake PHP framework welcome page should be visible. The URL should have the following format cakephp-mysql-example-validate.<app_domain>.
Once the functionality has been verified, the validate project can be deleted:
```
$ oc delete project validate
```
All resources within the project will be deleted as well.

Creating alerts using Prometheus

You can integrate OpenShift Container Platform with Prometheus to create visuals and alerts to help diagnose any environment issues before they arise. These issues can include if a node goes down, if a pod is consuming too much CPU or memory, and more.

See the Prometheus on OpenShift Container Platform section in the Installation and configuration guide for more information.

Prometheus on OpenShift Container Platform is a Technology Preview feature only. Technology Preview features are not supported with Red Hat production service level agreements (SLAs), might not be functionally complete, and Red Hat does not recommend to use them for production. These features provide early access to upcoming product features, enabling customers to test functionality and provide feedback during the development process.

For more information on Red Hat Technology Preview features support scope, see https://access.redhat.com/support/offerings/techpreview/.

Host health

To verify that the cluster is up and running, connect to a master instance, and run the following:

$ oc get nodes
NAME                  STATUS                     AGE       VERSION
ocp-infra-node-1clj   Ready                      1h        v1.6.1+5115d708d7
ocp-infra-node-86qr   Ready                      1h        v1.6.1+5115d708d7
ocp-infra-node-g8qw   Ready                      1h        v1.6.1+5115d708d7
ocp-master-94zd       Ready,SchedulingDisabled   1h        v1.6.1+5115d708d7
ocp-master-gjkm       Ready,SchedulingDisabled   1h        v1.6.1+5115d708d7
ocp-master-wc8w       Ready,SchedulingDisabled   1h        v1.6.1+5115d708d7
ocp-node-c5dg         Ready                      1h        v1.6.1+5115d708d7
ocp-node-ghxn         Ready                      1h        v1.6.1+5115d708d7
ocp-node-w135         Ready                      1h        v1.6.1+5115d708d7

The above cluster example consists of three master hosts, three infrastructure node hosts, and three node hosts. All of them are running. All hosts in the cluster should be visible in this output.

The Ready status means that master hosts can communicate with node hosts and that the nodes are ready to run pods (excluding the nodes in which scheduling is disabled).

Before you run etcd commands, source the etcd.conf file:

# source /etc/etcd/etcd.conf

You can check the basic etcd health status from any master instance with the etcdctl command:

# etcdctl --cert-file=$ETCD_PEER_CERT_FILE --key-file=$ETCD_PEER_KEY_FILE \
  --ca-file=/etc/etcd/ca.crt --endpoints=$ETCD_LISTEN_CLIENT_URLS cluster-health
member 59df5107484b84df is healthy: got healthy result from https://10.156.0.5:2379
member 6df7221a03f65299 is healthy: got healthy result from https://10.156.0.6:2379
member fea6dfedf3eecfa3 is healthy: got healthy result from https://10.156.0.9:2379
cluster is healthy

However, to get more information about etcd hosts, including the associated master host:

# etcdctl --cert-file=$ETCD_PEER_CERT_FILE --key-file=$ETCD_PEER_KEY_FILE \
  --ca-file=/etc/etcd/ca.crt --endpoints=$ETCD_LISTEN_CLIENT_URLS member list
295750b7103123e0: name=ocp-master-zh8d peerURLs=https://10.156.0.7:2380 clientURLs=https://10.156.0.7:2379 isLeader=true
b097a72f2610aea5: name=ocp-master-qcg3 peerURLs=https://10.156.0.11:2380 clientURLs=https://10.156.0.11:2379 isLeader=false
fea6dfedf3eecfa3: name=ocp-master-j338 peerURLs=https://10.156.0.9:2380 clientURLs=https://10.156.0.9:2379 isLeader=false

All etcd hosts should contain the master host name if the etcd cluster is co-located with master services, or all etcd instances should be visible if etcd is running separately.

etcdctl2 is an alias for the etcdctl tool that contains the proper flags to query the etcd cluster in v2 data model, as well as, etcdctl3 for v3 data model.

Router and registry health

To check if a router service is running:

$ oc -n default get deploymentconfigs/router
NAME      REVISION   DESIRED   CURRENT   TRIGGERED BY
router    1          3         3         config

The values in the DESIRED and CURRENT columns should match the number of nodes hosts.

Use the same command to check the registry status:

$ oc -n default get deploymentconfigs/docker-registry
NAME              REVISION   DESIRED   CURRENT   TRIGGERED BY
docker-registry   1          3         3         config

Multiple running instances of the container registry require backend storage supporting writes by multiple processes. If the chosen infrastructure provider does not contain this ability, running a single instance of a container registry is acceptable.

To verify that all pods are running and on which hosts:

$ oc -n default get pods -o wide
NAME                       READY     STATUS    RESTARTS   AGE       IP            NODE
docker-registry-1-54nhl    1/1       Running   0          2d        172.16.2.3    ocp-infra-node-tl47
docker-registry-1-jsm2t    1/1       Running   0          2d        172.16.8.2    ocp-infra-node-62rc
docker-registry-1-qbt4g    1/1       Running   0          2d        172.16.14.3   ocp-infra-node-xrtz
registry-console-2-gbhcz   1/1       Running   0          2d        172.16.8.4    ocp-infra-node-62rc
router-1-6zhf8             1/1       Running   0          2d        10.156.0.4    ocp-infra-node-62rc
router-1-ffq4g             1/1       Running   0          2d        10.156.0.10   ocp-infra-node-tl47
router-1-zqxbl             1/1       Running   0          2d        10.156.0.8    ocp-infra-node-xrtz

If OpenShift Container Platform is using an external container registry, the internal registry service does not need to be running.

Network connectivity

Network connectivity has two main networking layers: the cluster network for node interaction, and the software defined network (SDN) for pod interaction. OpenShift Container Platform supports multiple network configurations, often optimized for a specific infrastructure provider.

Due to the complexity of networking, not all verification scenarios are covered in this section.

Connectivity on master hosts

etcd and master hosts

master services keep their state synchronized using the etcd key-value store. Communication between master and etcd services is important, whether those etcd services are collocated on master hosts, or running on hosts designated only for the etcd service. This communication happens on TCP ports 2379 and 2380. See the Host health section for methods to check this communication.

SkyDNS

SkyDNS provides name resolution of local services running in OpenShift Container Platform. This service uses TCP and UDP port 8053.

To verify the name resolution:

$ dig +short docker-registry.default.svc.cluster.local
172.30.150.7

If the answer matches the output of the following, SkyDNS service is working correctly:

$ oc get svc/docker-registry -n default
NAME              CLUSTER-IP     EXTERNAL-IP   PORT(S)    AGE
docker-registry   172.30.150.7   <none>        5000/TCP   3d

API service and web console

Both the API service and web console share the same port, usually TCP 8443 or 443, depending on the setup. This port needs to be available within the cluster and to everyone who needs to work with the deployed environment. The URLs under which this port is reachable may differ for internal cluster and for external clients.

In the following example, the https://internal-master.example.com:443 URL is used by the internal cluster, and the https://master.example.com:443 URL is used by external clients. On any node host:

$ curl https://internal-master.example.com:443/version
{
  "major": "1",
  "minor": "6",
  "gitVersion": "v1.6.1+5115d708d7",
  "gitCommit": "fff65cf",
  "gitTreeState": "clean",
  "buildDate": "2017-10-11T22:44:25Z",
  "goVersion": "go1.7.6",
  "compiler": "gc",
  "platform": "linux/amd64"
}

This must be reachable from client’s network:

$ curl -k https://master.example.com:443/healthz
ok

Connectivity on node instances

The SDN connecting pod communication on nodes uses UDP port 4789 by default.

To verify node host functionality, create a new application. The following example ensures the node reaches the docker registry, which is running on an infrastructure node:

Procedure

Create a new project:
```
$ oc new-project sdn-test
```

Deploy an httpd application:

$ oc new-app centos/httpd-24-centos7~https://github.com/sclorg/httpd-ex

Wait until the build is complete:

$ oc get pods
NAME               READY     STATUS      RESTARTS   AGE
httpd-ex-1-205hz   1/1       Running     0          34s
httpd-ex-1-build   0/1       Completed   0          1m

Connect to the running pod:

$ oc rsh po/<pod-name>

For example:

$ oc rsh po/httpd-ex-1-205hz

Check the healthz path of the internal registry service:

$ curl -kv https://docker-registry.default.svc.cluster.local:5000/healthz
* About to connect() to docker-registry.default.svc.cluster.locl port 5000 (#0)
*   Trying 172.30.150.7...
* Connected to docker-registry.default.svc.cluster.local (172.30.150.7) port 5000 (#0)
* Initializing NSS with certpath: sql:/etc/pki/nssdb
* skipping SSL peer certificate verification
* SSL connection using TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256
* Server certificate:
* 	subject: CN=172.30.150.7
* 	start date: Nov 30 17:21:51 2017 GMT
* 	expire date: Nov 30 17:21:52 2019 GMT
* 	common name: 172.30.150.7
* 	issuer: CN=openshift-signer@1512059618
> GET /healthz HTTP/1.1
> User-Agent: curl/7.29.0
> Host: docker-registry.default.svc.cluster.local:5000
> Accept: */*
>
< HTTP/1.1 200 OK
< Cache-Control: no-cache
< Date: Mon, 04 Dec 2017 16:26:49 GMT
< Content-Length: 0
< Content-Type: text/plain; charset=utf-8
<
* Connection #0 to host docker-registry.default.svc.cluster.local left intact

sh-4.2$ *exit*

The HTTP/1.1 200 OK response means the node is correctly connecting.

Clean up the test project:

$ oc delete project sdn-test
project "sdn-test" deleted

The node host is listening on TCP port 10250. This port needs to be reachable by all master hosts on any node, and if monitoring is deployed in the cluster, the infrastructure nodes must have access to this port on all instances as well. Broken communication on this port can be detected with the following command:

$ oc get nodes
NAME                  STATUS                     AGE       VERSION
ocp-infra-node-1clj   Ready                      4d        v1.6.1+5115d708d7
ocp-infra-node-86qr   Ready                      4d        v1.6.1+5115d708d7
ocp-infra-node-g8qw   Ready                      4d        v1.6.1+5115d708d7
ocp-master-94zd       Ready,SchedulingDisabled   4d        v1.6.1+5115d708d7
ocp-master-gjkm       Ready,SchedulingDisabled   4d        v1.6.1+5115d708d7
ocp-master-wc8w       Ready,SchedulingDisabled   4d        v1.6.1+5115d708d7
ocp-node-c5dg         Ready                      4d        v1.6.1+5115d708d7
ocp-node-ghxn         Ready                      4d        v1.6.1+5115d708d7
ocp-node-w135         NotReady                   4d        v1.6.1+5115d708d7

In the output above, the node service on the ocp-node-w135 node is not reachable by the master services, which is represented by its NotReady status.

The last service is the router, which is responsible for routing connections to the correct services running in the OpenShift Container Platform cluster. Routers listen on TCP ports 80 and 443 on infrastructure nodes for ingress traffic. Before routers can start working, DNS must be configured:

$ dig *.apps.example.com

; <<>> DiG 9.11.1-P3-RedHat-9.11.1-8.P3.fc27 <<>> *.apps.example.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 45790
;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;*.apps.example.com.	IN	A

;; ANSWER SECTION:
*.apps.example.com. 3571	IN	CNAME	apps.example.com.
apps.example.com.	3561	IN	A	35.xx.xx.92

;; Query time: 0 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Tue Dec 05 16:03:52 CET 2017
;; MSG SIZE  rcvd: 105

The IP address, in this case 35.xx.xx.92, should be pointing to the load balancer distributing ingress traffic to all infrastructure nodes. To verify the functionality of the routers, check the registry service once more, but this time from outside the cluster:

$ curl -kv https://docker-registry-default.apps.example.com/healthz
*   Trying 35.xx.xx.92...
* TCP_NODELAY set
* Connected to docker-registry-default.apps.example.com (35.xx.xx.92) port 443 (#0)
...
< HTTP/2 200
< cache-control: no-cache
< content-type: text/plain; charset=utf-8
< content-length: 0
< date: Tue, 05 Dec 2017 15:13:27 GMT
<
* Connection #0 to host docker-registry-default.apps.example.com left intact

Storage

master instances need at least 40 GB of hard disk space for the /var directory. Check the disk usage of a master host using the df command:

$ df -hT
Filesystem     Type      Size  Used Avail Use% Mounted on
/dev/sda1      xfs        45G  2.8G   43G   7% /
devtmpfs       devtmpfs  3.6G     0  3.6G   0% /dev
tmpfs          tmpfs     3.6G     0  3.6G   0% /dev/shm
tmpfs          tmpfs     3.6G   63M  3.6G   2% /run
tmpfs          tmpfs     3.6G     0  3.6G   0% /sys/fs/cgroup
tmpfs          tmpfs     732M     0  732M   0% /run/user/1000
tmpfs          tmpfs     732M     0  732M   0% /run/user/0

Node instances need at least 15 GB space for the /var directory, and at least another 15 GB for Docker storage (/var/lib/docker in this case). Depending on the size of the cluster and the amount of ephemeral storage desired for pods, a separate partition should be created for /var/lib/origin/openshift.local.volumes on the nodes.

$ df -hT
Filesystem     Type      Size  Used Avail Use% Mounted on
/dev/sda1      xfs        25G  2.4G   23G  10% /
devtmpfs       devtmpfs  3.6G     0  3.6G   0% /dev
tmpfs          tmpfs     3.6G     0  3.6G   0% /dev/shm
tmpfs          tmpfs     3.6G  147M  3.5G   4% /run
tmpfs          tmpfs     3.6G     0  3.6G   0% /sys/fs/cgroup
/dev/sdb       xfs        25G  2.7G   23G  11% /var/lib/docker
/dev/sdc       xfs        50G   33M   50G   1% /var/lib/origin/openshift.local.volumes
tmpfs          tmpfs     732M     0  732M   0% /run/user/1000

Persistent storage for pods should be handled outside of the instances running the OpenShift Container Platform cluster. Persistent volumes for pods can be provisioned by the infrastructure provider, or with the use of container native storage or container ready storage.

Docker storage

Docker Storage can be backed by one of two options. The first is a thin pool logical volume with device mapper, the second, since Red Hat Enterprise Linux version 7.4, is an overlay2 file system. The overlay2 file system is generally recommended due to the ease of setup and increased performance.

The Docker storage disk is mounted as /var/lib/docker and formatted with xfs file system. Docker storage is configured to use overlay2 filesystem:

$ cat /etc/sysconfig/docker-storage
DOCKER_STORAGE_OPTIONS='--storage-driver overlay2'

To verify this storage driver is used by Docker:

# docker info
Containers: 4
 Running: 4
 Paused: 0
 Stopped: 0
Images: 4
Server Version: 1.12.6
Storage Driver: overlay2
 Backing Filesystem: xfs
Logging Driver: journald
Cgroup Driver: systemd
Plugins:
 Volume: local
 Network: overlay host bridge null
 Authorization: rhel-push-plugin
Swarm: inactive
Runtimes: docker-runc runc
Default Runtime: docker-runc
Security Options: seccomp selinux
Kernel Version: 3.10.0-693.11.1.el7.x86_64
Operating System: Employee SKU
OSType: linux
Architecture: x86_64
Number of Docker Hooks: 3
CPUs: 2
Total Memory: 7.147 GiB
Name: ocp-infra-node-1clj
ID: T7T6:IQTG:WTUX:7BRU:5FI4:XUL5:PAAM:4SLW:NWKL:WU2V:NQOW:JPHC
Docker Root Dir: /var/lib/docker
Debug Mode (client): false
Debug Mode (server): false
Registry: https://registry.access.redhat.com/v1/
WARNING: bridge-nf-call-iptables is disabled
WARNING: bridge-nf-call-ip6tables is disabled
Insecure Registries:
 127.0.0.0/8
Registries: registry.access.redhat.com (secure), registry.access.redhat.com (secure), docker.io (secure)

API service status

The OpenShift API service, atomic-openshift-master-api.service, runs on all master instances. To see the status of the service:

$ systemctl status atomic-openshift-master-api.service
● atomic-openshift-master-api.service - Atomic OpenShift master API
   Loaded: loaded (/usr/lib/systemd/system/atomic-openshift-master-api.service; enabled; vendor preset: disabled)
   Active: active (running) since Thu 2017-11-30 11:40:19 EST; 5 days ago
     Docs: https://github.com/openshift/origin
 Main PID: 30047 (openshift)
   Memory: 65.0M
   CGroup: /system.slice/atomic-openshift-master-api.service
           └─30047 /usr/bin/openshift start master api --config=/etc/origin/master/ma...

Dec 06 09:15:49 ocp-master-94zd atomic-openshift-master-api[30047]: I1206 09:15:49.85...
Dec 06 09:15:50 ocp-master-94zd atomic-openshift-master-api[30047]: I1206 09:15:50.96...
Dec 06 09:15:52 ocp-master-94zd atomic-openshift-master-api[30047]: I1206 09:15:52.34...

The API service exposes a health check, which can be queried externally with:

$ curl -k https://master.example.com/healthz
ok

Controller role verification

The OpenShift Container Platform controller service, atomic-openshift-master-controllers.service, is available across all master hosts. The service runs in active/passive mode, meaning it should only be running on one master at any time.

The OpenShift Container Platform controllers execute a procedure to choose which host runs the service. The current running value is stored in an annotation in a special configmap stored in the kube-system project.

Verify the master host running the atomic-openshift-master-controllers service as a cluster-admin user:

$ oc get -n kube-system cm openshift-master-controllers -o yaml
apiVersion: v1
kind: ConfigMap
metadata:
  annotations:
    control-plane.alpha.kubernetes.io/leader: '{"holderIdentity":"master-ose-master-0.example.com-10.19.115.212-dnwrtcl4","leaseDurationSeconds":15,"acquireTime":"2018-02-17T18:16:54Z","renewTime":"2018-02-19T13:50:33Z","leaderTransitions":16}'
  creationTimestamp: 2018-02-02T10:30:04Z
  name: openshift-master-controllers
  namespace: kube-system
  resourceVersion: "17349662"
  selfLink: /api/v1/namespaces/kube-system/configmaps/openshift-master-controllers
  uid: 08636843-0804-11e8-8580-fa163eb934f0

The command outputs the current master controller in the control-plane.alpha.kubernetes.io/leader annotation, within the holderIdentity property as:

master-<hostname>-<ip>-<8_random_characters>

Find the hostname of the master host by filtering the output using the following:

$ oc get -n kube-system cm openshift-master-controllers -o json | jq -r '.metadata.annotations[] | fromjson.holderIdentity | match("^master-(.*)-[0-9.]*-[0-9a-z]{8}$") | .captures[0].string'
ose-master-0.example.com

Verifying correct Maximum Transmission Unit (MTU) size

Verifying the maximum transmission unit (MTU) prevents a possible networking misconfiguration that can masquerade as an SSL certificate issue.

When a packet is larger than the MTU size that is transmitted over HTTP, the physical network router is able to break the packet into multiple packets to transmit the data. However, when a packet is larger than the MTU size is that transmitted over HTTPS, the router is forced to drop the packet.

Installation produces certificates that provide secure connections to multiple components that include:

master hosts
node hosts
infrastructure nodes
registry
router

These certificates can be found within the /etc/origin/master directory for the master nodes and /etc/origin/node directory for the infra and app nodes.

After installation, you can verify connectivity to the REGISTRY_OPENSHIFT_SERVER_ADDR using the process outlined in the Network connectivity section.

Prerequisites

From a master host, get the HTTPS address:

$ oc get dc docker-registry -o jsonpath='{.spec.template.spec.containers[].env[?(@.name=="OPENSHIFT_DEFAULT_REGISTRY")].value}{"\n"}'
docker-registry.default.svc:5000

The above gives the output of docker-registry.default.svc:5000.

Append /healthz to the value given above, use it to check on all hosts (master, infrastructure, node):

$ curl -v https://docker-registry.default.svc:5000/healthz
* About to connect() to docker-registry.default.svc port 5000 (#0)
*   Trying 172.30.11.171...
* Connected to docker-registry.default.svc (172.30.11.171) port 5000 (#0)
* Initializing NSS with certpath: sql:/etc/pki/nssdb
*   CAfile: /etc/pki/tls/certs/ca-bundle.crt
  CApath: none
* SSL connection using TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256
* Server certificate:
* 	subject: CN=172.30.11.171
* 	start date: Oct 18 05:30:10 2017 GMT
* 	expire date: Oct 18 05:30:11 2019 GMT
* 	common name: 172.30.11.171
* 	issuer: CN=openshift-signer@1508303629
> GET /healthz HTTP/1.1
> User-Agent: curl/7.29.0
> Host: docker-registry.default.svc:5000
> Accept: */*
>
< HTTP/1.1 200 OK
< Cache-Control: no-cache
< Date: Tue, 24 Oct 2017 19:42:35 GMT
< Content-Length: 0
< Content-Type: text/plain; charset=utf-8
<
* Connection #0 to host docker-registry.default.svc left intact

The above example output shows the MTU size being used to ensure the SSL connection is correct. The attempt to connect is successful, followed by connectivity being established and completes with initializing the NSS with the certpath and all the server certificate information regarding the docker-registry.

An improper MTU size results in a timeout:

$ curl -v https://docker-registry.default.svc:5000/healthz
* About to connect() to docker-registry.default.svc port 5000 (#0)
*   Trying 172.30.11.171...
* Connected to docker-registry.default.svc (172.30.11.171) port 5000 (#0)
* Initializing NSS with certpath: sql:/etc/pki/nssdb

The above example shows that the connection is established, but it cannot finish initializing NSS with certpath. The issue deals with improper MTU size set within the /etc/origin/node/node-config.yaml file.

To fix this issue, adjust the MTU size within the /etc/origin/node/node-config.yaml to 50 bytes smaller than the MTU size being used by the OpenShift SDN Ethernet device.

View the MTU size of the desired Ethernet device (i.e. eth0):

$ ip link show eth0
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT qlen 1000
    link/ether fa:16:3e:92:6a:86 brd ff:ff:ff:ff:ff:ff

The above shows MTU set to 1500.

To change the MTU size, modify the /etc/origin/node/node-config.yaml file and set a value that is 50 bytes smaller than output provided by the ip command.

For example, if the MTU size is set to 1500, adjust the MTU size to 1450 within the /etc/origin/node/node-config.yaml file:
```
networkConfig:
   mtu: 1450
```

Save the changes and reboot the node:

You must change the MTU size on all masters and nodes that are part of the OpenShift Container Platform SDN. Also, the MTU size of the tun0 interface must be the same across all nodes that are part of the cluster.

Once the node is back online, confirm the issue no longer exists by re-running the original curl command.
```
$ curl -v https://docker-registry.default.svc:5000/healthz
```
If the timeout persists, continue to adjust the MTU size in increments of 50 bytes and repeat the process.