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split out the 'declarative/imperative' explanation
This commit is contained in:
Jérôme Petazzoni
63
slides/common/declarative.md
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63
slides/common/declarative.md
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# Declarative vs imperative
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- Our container orchestrator puts a very strong emphasis on being *declarative*
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- Declarative:
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*I would like a cup of tea.*
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- Imperative:
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*Boil some water. Pour it in a teapot. Add tea leaves. Steep for a while. Serve in cup.*
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--
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- Declarative seems simpler at first ...
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--
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- ... As long as you know how to brew tea
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---
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## Declarative vs imperative
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- What declarative would really be:
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*I want a cup of tea, obtained by pouring an infusion¹ of tea leaves in a cup.*
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--
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*¹An infusion is obtained by letting the object steep a few minutes in hot² water.*
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--
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*²Hot liquid is obtained by pouring it in an appropriate container³ and setting it on a stove.*
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--
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*³Ah, finally, containers! Something we know about. Let's get to work, shall we?*
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--
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.footnote[Did you know there was an [ISO standard](https://en.wikipedia.org/wiki/ISO_3103)
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specifying how to brew tea?]
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---
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## Declarative vs imperative
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- Imperative systems:
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- simpler
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- if a task is interrupted, we have to restart from scratch
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- Declarative systems:
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- if a task is interrupted (or if we show up to the party half-way through),
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we can figure out what's missing and do only what's necessary
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- we need to be able to *observe* the system
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- ... and compute a "diff" between *what we have* and *what we want*
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@@ -19,6 +19,8 @@ chapters:
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- swarm/versions.md
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- common/sampleapp.md
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- swarm/swarmkit.md
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- common/declarative.md
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- swarm/swarmmode.md
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- swarm/creatingswarm.md
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- swarm/morenodes.md
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- - swarm/firstservice.md
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@@ -17,6 +17,8 @@ chapters:
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- kube/versions-k8s.md
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- common/sampleapp.md
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- - kube/concepts-k8s.md
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- common/declarative.md
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- kube/declarative.md
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- kube/kubenet.md
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- kube/kubectlget.md
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- kube/setup-k8s.md
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@@ -211,86 +211,3 @@ class: pic
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(Diagram courtesy of Weave Works, used with permission.)
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---
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# Declarative vs imperative
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- Kubernetes puts a very strong emphasis on being *declarative*
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- Declarative:
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*I would like a cup of tea.*
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- Imperative:
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*Boil some water. Pour it in a teapot. Add tea leaves. Steep for a while. Serve in cup.*
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--
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- Declarative seems simpler at first ...
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--
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- ... As long as you know how to brew tea
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---
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## Declarative vs imperative
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- What declarative would really be:
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*I want a cup of tea, obtained by pouring an infusion¹ of tea leaves in a cup.*
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--
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*¹An infusion is obtained by letting the object steep a few minutes in hot² water.*
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--
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*²Hot liquid is obtained by pouring it in an appropriate container³ and setting it on a stove.*
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--
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*³Ah, finally, containers! Something we know about. Let's get to work, shall we?*
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--
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.footnote[Did you know there was an [ISO standard](https://en.wikipedia.org/wiki/ISO_3103)
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specifying how to brew tea?]
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---
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## Declarative vs imperative
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- Imperative systems:
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- simpler
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- if a task is interrupted, we have to restart from scratch
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- Declarative systems:
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- if a task is interrupted (or if we show up to the party half-way through),
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we can figure out what's missing and do only what's necessary
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- we need to be able to *observe* the system
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- ... and compute a "diff" between *what we have* and *what we want*
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---
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## Declarative vs imperative in Kubernetes
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- Virtually everything we create in Kubernetes is created from a *spec*
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- Watch for the `spec` fields in the YAML files later!
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- The *spec* describes *how we want the thing to be*
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- Kubernetes will *reconcile* the current state with the spec
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<br/>(technically, this is done by a number of *controllers*)
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- When we want to change some resource, we update the *spec*
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- Kubernetes will then *converge* that resource
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14
slides/kube/declarative.md
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14
slides/kube/declarative.md
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@@ -0,0 +1,14 @@
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## Declarative vs imperative in Kubernetes
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- Virtually everything we create in Kubernetes is created from a *spec*
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- Watch for the `spec` fields in the YAML files later!
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- The *spec* describes *how we want the thing to be*
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- Kubernetes will *reconcile* the current state with the spec
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<br/>(technically, this is done by a number of *controllers*)
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- When we want to change some resource, we update the *spec*
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- Kubernetes will then *converge* that resource
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@@ -19,6 +19,8 @@ chapters:
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- swarm/versions.md
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- common/sampleapp.md
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- swarm/swarmkit.md
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- common/declarative.md
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- swarm/swarmmode.md
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- swarm/creatingswarm.md
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- swarm/morenodes.md
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- - swarm/firstservice.md
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@@ -22,6 +22,8 @@ chapters:
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Part 1
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- common/sampleapp.md
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- swarm/swarmkit.md
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- common/declarative.md
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- swarm/swarmmode.md
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- swarm/creatingswarm.md
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- swarm/machine.md
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- swarm/morenodes.md
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@@ -118,52 +118,3 @@ class: pic
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- *Nodes* know which *tasks* should be running, and will start or stop containers accordingly (through the Docker Engine API)
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You can refer to the [NOMENCLATURE](https://github.com/docker/swarmkit/blob/master/design/nomenclature.md) in the SwarmKit repo for more details.
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---
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## Swarm Mode
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- Since version 1.12, Docker Engine embeds SwarmKit
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- All the SwarmKit features are "asleep" until you enable "Swarm Mode"
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- Examples of Swarm Mode commands:
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- `docker swarm` (enable Swarm mode; join a Swarm; adjust cluster parameters)
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- `docker node` (view nodes; promote/demote managers; manage nodes)
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- `docker service` (create and manage services)
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???
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- The Docker API exposes the same concepts
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- The SwarmKit API is also exposed (on a separate socket)
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---
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## You need to enable Swarm mode to use the new stuff
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- By default, all this new code is inactive
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- Swarm Mode can be enabled, "unlocking" SwarmKit functions
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<br/>(services, out-of-the-box overlay networks, etc.)
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.exercise[
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- Try a Swarm-specific command:
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```bash
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docker node ls
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```
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<!-- Ignore errors: ```wait ``` -->
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]
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--
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You will get an error message:
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```
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Error response from daemon: This node is not a swarm manager. [...]
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```
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46
slides/swarm/swarmmode.md
Normal file
46
slides/swarm/swarmmode.md
Normal file
@@ -0,0 +1,46 @@
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# Swarm Mode
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- Since version 1.12, Docker Engine embeds SwarmKit
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- All the SwarmKit features are "asleep" until you enable "Swarm Mode"
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- Examples of Swarm Mode commands:
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- `docker swarm` (enable Swarm mode; join a Swarm; adjust cluster parameters)
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- `docker node` (view nodes; promote/demote managers; manage nodes)
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- `docker service` (create and manage services)
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???
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- The Docker API exposes the same concepts
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- The SwarmKit API is also exposed (on a separate socket)
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---
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## You need to enable Swarm mode to use the new stuff
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- By default, all this new code is inactive
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- Swarm Mode can be enabled, "unlocking" SwarmKit functions
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<br/>(services, out-of-the-box overlay networks, etc.)
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.exercise[
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- Try a Swarm-specific command:
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```bash
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docker node ls
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```
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<!-- Ignore errors: ```wait ``` -->
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]
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--
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You will get an error message:
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```
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Error response from daemon: This node is not a swarm manager. [...]
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```
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