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Co-authored-by: Tim Bannister <tim@scalefactory.com>
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Antonio Ojea 2022-11-29 15:26:26 +00:00 committed by GitHub
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content/en/docs/concepts/services-networking/cluster-ip-allocation.md
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@ -20,7 +20,8 @@ Service across the different backing Pods.
## How Service ClusterIPs are allocated?
A Service `ClusterIP` can be assigned:
When Kubernetes needs to assign a virtual IP address for a Service,
that assignment happens one of two ways:
_dynamically_
: the cluster's control plane automatically picks a free IP address from within the configured IP range for `type: ClusterIP` Services.
@ -37,7 +38,7 @@ been allocated will return an error.
Sometimes you may want to have Services running in well-known IP addresses, so other components and
users in the cluster can use them.
The best example is the DNS Service for the cluster. Some Kubernetes installers assign the 10th address from
The best example is the DNS Service for the cluster. As a soft convention, some Kubernetes installers assign the 10th IP address from
the Service IP range to the DNS service. Assuming you configured your cluster with Service IP range
10.96.0.0/16 and you want your DNS Service IP to be 10.96.0.10, you'd have to create a Service like
this:
@ -84,9 +85,12 @@ Dynamic IP assignment uses the upper band by default, once this has been exhaust
use the lower range. This will allow users to use static allocations on the lower band with a low
risk of collision.
Examples:
## Examples {#allocation-examples}
#### Service IP CIDR block: 10.96.0.0/24
### Example 1 {#allocation-example-1}
This example uses the IP address range: 10.96.0.0/24 (CIDR notation) for the IP addresses
of Services.
Range Size: 2<sup>8</sup> - 2 = 254
Band Offset: `min(max(16, 256/16), 256)` = `min(16, 256)` = 16
@ -101,7 +105,10 @@ pie showData
"Dynamic" : 238
{{< /mermaid >}}
#### Service IP CIDR block: 10.96.0.0/20
### Example 2 {#allocation-example-2}
This example uses the IP address range: 10.96.0.0/20 (CIDR notation) for the IP addresses
of Services.
Range Size: 2<sup>12</sup> - 2 = 4094
Band Offset: `min(max(16, 4096/16), 256)` = `min(256, 256)` = 256
@ -116,7 +123,10 @@ pie showData
"Dynamic" : 3838
{{< /mermaid >}}
#### Service IP CIDR block: 10.96.0.0/16
### Example 3 {#allocation-example-3}
This example uses the IP address range: 10.96.0.0/16 (CIDR notation) for the IP addresses
of Services.
Range Size: 2<sup>16</sup> - 2 = 65534
Band Offset: `min(max(16, 65536/16), 256)` = `min(4096, 256)` = 256