WEBVTT 00:00.120 --> 00:07.410 .In this lecture we will discuss about the part to note relationship and how you can restrict what parts 00:07.500 --> 00:15.820 are placed on what notes the concept of teens and toleration can be a bit confusing for beginners. 00:15.870 --> 00:22.710 So we will try to understand what they are using an analogy of a bug approaching a person. 00:22.710 --> 00:29.480 Now my apologies in advance but this is the best I could come up with to prevent the bug from landing 00:29.570 --> 00:30.800 on the person. 00:31.010 --> 00:36.820 We spray the person with a repellent spray or attained as we will call it. 00:36.860 --> 00:41.750 In this lecture the book is intolerant to the smell. 00:41.750 --> 00:50.350 So on approaching the person detained applied on the person throws the bug off however there could be 00:50.470 --> 00:56.920 other books that are tolerant to the smell and so the taint doesn't really affect them. 00:57.150 --> 01:00.370 And so they end up landing on the person. 01:00.370 --> 01:05.330 So there are two things that decide if a bug can land on a person. 01:05.530 --> 01:08.080 First the taint on the person. 01:08.290 --> 01:15.310 And second the bugs toleration level to that particular taint getting back to Cuba. 01:15.310 --> 01:20.420 NET is the person is a node and the bugs are pods. 01:20.430 --> 01:27.230 Now teens and toleration have nothing to do with security or intrusion on the Cluster. 01:27.560 --> 01:33.800 Teens and toleration are used to set restrictions on what parts can be scheduled. 01:33.860 --> 01:41.510 On a note let us start with a simple cluster with three worker notes the notes are named one two and 01:41.510 --> 01:42.390 three. 01:42.440 --> 01:46.420 We also have a set of paths that are to be deployed on these notes. 01:46.490 --> 01:48.710 Let's call them A B C and D. 01:49.010 --> 01:55.410 When the parts are created common it is scheduler tries to place these parts on the available worker 01:55.430 --> 01:56.560 nodes. 01:56.690 --> 02:04.130 As of now there are no restrictions are limitations and as such the scheduler places the parts across 02:04.220 --> 02:06.910 all of the nodes to balance them out equally. 02:08.120 --> 02:15.510 Now let us assume that we have dedicated resources on Node 1 for a particular use case or application 02:16.520 --> 02:23.230 so we would like only those parts that belong to this application to be placed on Node 1. 02:23.310 --> 02:30.300 First we prevent all parts from being placed on the Node by placing a taint on the Node. 02:30.900 --> 02:33.910 Let's call it blue by default. 02:33.980 --> 02:43.510 Paths have no toleration which means unless specified otherwise none of the parts can tolerate any taint. 02:43.510 --> 02:50.260 So in this case none of the parts can be placed on Node 1 as none of them can tolerate the team. 02:50.270 --> 02:59.170 Blue this solves half of our requirement no unwanted parts are going to be placed on this note. 02:59.360 --> 03:04.100 The other half is to enable certain parts to be placed on this note. 03:05.930 --> 03:11.860 For this we must specify which parts are tolerant to this particular attempt. 03:12.050 --> 03:20.840 In our case we would like to allow only Part D to be placed on this note so we add a toleration to Part 03:20.960 --> 03:21.290 D. 03:22.280 --> 03:30.260 Part D is now tolerant to blue so when the scheduler tries to place this part on Node 1 it goes through 03:30.650 --> 03:35.960 Node 1 can now only accept parts that can tolerate the taint. 03:35.990 --> 03:40.740 Blue so with all the teens and toleration is in place. 03:40.850 --> 03:44.100 This is how the parts would be scheduled. 03:44.180 --> 03:50.450 The scheduler tries to place part a on not one but due to the team it is thrown off and it goes to note 03:50.450 --> 03:57.440 to the scheduler then tries to place part B on not one but again due to the taint it is thrown off and 03:57.440 --> 04:01.490 is placed on Node 3 which happens to be the next free node. 04:01.490 --> 04:07.420 The scheduler then tries to place part c to the Node 1 it is thrown off again and ends up on Node 2. 04:07.460 --> 04:14.520 Finally the scheduler tries to place part D on Node 1 since the part is tolerant to Node 1. 04:14.540 --> 04:22.540 It goes through so remember trains are set on nodes and toleration are set on pods. 04:22.690 --> 04:24.330 So how do you do this. 04:24.430 --> 04:31.750 Use the cube control taint nodes command to taint in node specify the name of the node to train followed 04:31.750 --> 04:35.260 by the train itself which is a key value pair. 04:35.320 --> 04:42.550 For example if you would like to dedicate the Node 2 parts in application blue then the key value pair 04:42.550 --> 04:49.820 would be ab equals blue the taint effect defines what would happen to the pods. 04:49.840 --> 04:58.120 If they do not tolerate the taint there are three taint effects no schedule which means the parts will 04:58.120 --> 05:02.030 not be scheduled on the node which is what we have been discussing. 05:02.220 --> 05:08.950 Prefer No schedule which means the system will try to avoid placing a part on the node but that is not 05:08.950 --> 05:10.520 guaranteed. 05:10.570 --> 05:12.790 And third is no execute. 05:13.000 --> 05:21.010 Which means that new parts will not be scheduled on the node and existing parts on the node if any will 05:21.010 --> 05:24.700 be evicted if they do not tolerate the taint. 05:24.700 --> 05:31.000 These parts may have been scheduled on Node before the 10th was applied to the node. 05:31.030 --> 05:38.200 An example command would be detained Node node one with the key value pair app equals blue and an effect 05:38.470 --> 05:46.440 of no schedule toleration is are added to parts to add a toleration to a pod. 05:46.450 --> 05:52.980 First pull up the pod definition file in the spec section of the pod definition file had a section called 05:53.010 --> 05:59.530 toleration move the same values used to while creating the taint under this section. 05:59.580 --> 06:07.830 The key is app operator is equal value is blue and the effect is no should you. 06:07.890 --> 06:13.810 And remember all of these values need to be encoded in double codes. 06:14.100 --> 06:21.690 When the pods are now created or updated with the new toleration they are either not scheduled on nodes 06:21.900 --> 06:29.780 or evicted from the existing nodes depending on the effect set let us try to understand the No. 06:29.790 --> 06:33.600 Execute takes effect in a bit more depth. 06:33.960 --> 06:37.380 In this example we have three nodes running some workload. 06:37.380 --> 06:43.440 We do not have any teens or toleration at this point so they are scheduled this way. 06:43.440 --> 06:51.420 We then decided to dedicate Node 1 for a special application and as such we obtained the node with the 06:51.420 --> 06:58.380 application name and add a toleration to the part that belongs to the application which happens to be 06:58.380 --> 06:59.280 part D. 06:59.280 --> 07:06.560 In this case while tending the node we set the taint effect to no execute and as such. 07:06.750 --> 07:14.190 Once detained on the Node takes effect it evokes Part C from the node which simply means that the part 07:14.220 --> 07:15.170 is killed. 07:15.360 --> 07:20.930 The Part D continues to run on the node as it has a toleration to the change. 07:22.030 --> 07:26.980 Now going back to our original scenario where we have teens and toleration is configured. 07:27.070 --> 07:35.500 Remember teens and toleration are only meant to restrict nodes from accepting certain parts. 07:35.500 --> 07:45.160 In this case no one can only accept Part D but it does not guarantee that Part D will always be placed 07:45.220 --> 07:46.400 on Node 1. 07:46.480 --> 07:53.800 Since there are no teens or restrictions applied on the other two nodes Part D may very well be placed 07:53.830 --> 08:02.350 on any of the other two nodes so remember teens and toleration does not tell the part to go to a particular 08:02.440 --> 08:03.140 node. 08:03.160 --> 08:09.460 Instead it tells the node to only accept parts with certain toleration. 08:10.150 --> 08:17.950 If your requirement is to restrict a part to certain nodes it is achieved through another concept called 08:17.980 --> 08:23.410 Ask node affinity which we will discuss in the next lecture finally. 08:23.510 --> 08:28.200 While we're on this topic let us also take a look at an interesting fact. 08:28.460 --> 08:32.650 So far we have only been referring to the worker nodes. 08:32.670 --> 08:39.290 But we also have master nodes in the cluster which is technically just another note that has all the 08:39.290 --> 08:41.780 capabilities of hosting a part. 08:41.790 --> 08:45.350 Plus it runs all the management software. 08:45.470 --> 08:52.430 Now I'm not sure if you noticed the scheduler does not schedule any part on the master node. 08:52.430 --> 08:56.590 Why is that when the covenant is cluster is first setup. 08:56.630 --> 09:03.530 It teams is set on the master node automatically that prevents any parts from being schedule on this 09:03.530 --> 09:04.250 note. 09:04.580 --> 09:08.670 You can see this as well as modified his behavior if required. 09:08.990 --> 09:17.330 However a best practice is to not deploy application workloads on a master server to see this taint 09:17.540 --> 09:18.340 run a cube. 09:18.340 --> 09:26.420 Control described node command with Cube master as the node name and look for the tail section. 09:26.540 --> 09:32.200 You will see a taint set to not schedule any parts on the master node. 09:32.270 --> 09:34.310 Well that's it for this lecture. 09:34.310 --> 09:39.320 Head over to the coding exercises section and practice working with teens and toleration is.