1 00:00:00,630 --> 00:00:03,270 Hello and welcome to this lecture. 2 00:00:03,270 --> 00:00:04,540 My name is Mumshad 3 00:00:04,560 --> 00:00:14,180 Mannambath. Let us look at a 3 Node Kubernetes cluster. Each node has a set of CPU, Memory and Disk 4 00:00:14,180 --> 00:00:15,890 resources available. 5 00:00:16,310 --> 00:00:19,190 Every POD consumes a set of resources. 6 00:00:19,190 --> 00:00:27,470 In this case 2 CPUs , one Memory and some disk space. Whenever a POD is placed on a Node, it consumes resources 7 00:00:27,620 --> 00:00:35,330 available to that node. As we have discussed before, it is the kubernetes scheduler that decides which 8 00:00:35,330 --> 00:00:43,380 Node a POD goes to. The scheduler takes into consideration, the amount of resources required by a POD 9 00:00:43,760 --> 00:00:51,170 and those available on the Nodes. In this case, the scheduler schedules a new POD on Node 2. If the node 10 00:00:51,170 --> 00:00:58,370 has no sufficient resources, the scheduler avoids placing the POD on that node Instead places the POD 11 00:00:58,460 --> 00:01:05,060 on one where sufficient resources are available if there is no sufficient resources available on any 12 00:01:05,060 --> 00:01:10,970 of the nodes, Kubernetes holds back scheduling the POD, and you will see the POD in a pending state. 13 00:01:11,450 --> 00:01:19,550 If you look at the events, you will see the reason – insufficient cpu. Let us now focus on the resource 14 00:01:19,550 --> 00:01:25,740 resource requirements for each POD. What are these blocks and what are their values? 15 00:01:25,740 --> 00:01:33,750 By default, kubernetes assumes that a POD or a container within a POD requires .5 CPU & 16 00:01:33,750 --> 00:01:37,310 256 Mebibyte of memory. 17 00:01:37,410 --> 00:01:44,790 This is known as the resource request for a container the minimum amount of CPU or memory requested 18 00:01:44,790 --> 00:01:49,630 by the container when the scheduler tries to place the pod on a node. 19 00:01:49,650 --> 00:01:55,740 It uses these numbers to identify a node which has sufficient amount of resources available. 20 00:01:56,160 --> 00:02:02,760 Now if you know that your application will need more than these you can modify these values by specifying 21 00:02:02,760 --> 00:02:09,370 them in your pod or deployment definition files in the simple pod definition file. 22 00:02:09,480 --> 00:02:18,260 add a section called resources, under which add requests and specify the new values for memory and cpu usage. 23 00:02:18,480 --> 00:02:24,600 In this case I set it to 1GB of memory and 1 count of vCPU. 24 00:02:24,660 --> 00:02:28,060 So what does 1 count of CPU really mean? 25 00:02:28,200 --> 00:02:33,010 Remember these blocks are used for illustration purposes only. 26 00:02:33,030 --> 00:02:36,440 It doesn't have to be in the increment of point five. 27 00:02:36,570 --> 00:02:42,570 You can specify any value as low as 0.1. 0.1 28 00:02:42,600 --> 00:02:49,720 CPU can also be expressed as 100m were m stands for milli. 29 00:02:49,920 --> 00:02:59,400 You can go as low as 1m, but not lower than that. 1 count of CPU is equivalent to 1 vCPU. 30 00:02:59,400 --> 00:03:09,510 That’s 1 vCPU in AWS, or 1 Core in GCP or Azure or 1 Hyperthread. You could request a higher number 31 00:03:09,510 --> 00:03:16,800 of CPUs for the container, provided your Nodes are sufficiently funded. Similarly, with memory you could 32 00:03:16,800 --> 00:03:26,470 specify 256 Mebibyte using the Mi suffix. Or specify the same value in Memory like this. Or use the 33 00:03:26,470 --> 00:03:29,130 suffix G for a gigabyte. 34 00:03:29,140 --> 00:03:37,450 Note the difference between G and Gi. G is Gigabyte and it refers to a 1000 Megabytes, whereas Gi 35 00:03:37,450 --> 00:03:44,540 Gi refers to Gibibyte and refers to 1024 Mebibyte. 36 00:03:44,590 --> 00:03:47,970 The same applies to megabyte and kilobytes. 37 00:03:48,580 --> 00:03:55,000 Let's now look at a container running on a node in the docker world a docker container has no limit 38 00:03:55,090 --> 00:04:02,680 to the resources it can consume on a Node. Say a container starts with 1 vCPU on a Node, it can go up 39 00:04:02,860 --> 00:04:10,060 and consume as much resource as it requires, suffocating the native processes on the node or other containers 40 00:04:10,210 --> 00:04:11,740 of resources. 41 00:04:11,770 --> 00:04:17,800 However you can set a limit for the resource usage on these pods by default. 42 00:04:17,980 --> 00:04:26,830 Kubernetes sets a limit of 1vCPU to containers. So if you do not specify explicitly, a container will be limited 43 00:04:26,920 --> 00:04:30,520 to consume only 1 vCPU from the Node. 44 00:04:30,520 --> 00:04:37,810 The same goes with memory. By default, kubernetes sets a limit of 512 Mebibyte on containers. 45 00:04:38,260 --> 00:04:44,200 if you don't like the default limit you can change them by adding a limit section under the resources 46 00:04:44,200 --> 00:04:51,460 section in your pod definition file. Specify new limits for memory and cpu you like this when the 47 00:04:51,460 --> 00:04:55,960 pod is created, kubernetes sets new limits for the container. 48 00:04:55,960 --> 00:05:02,580 Remember that the limits and requests are set for each container within the pod. 49 00:05:02,650 --> 00:05:08,470 So what happens when a pod tries to exceed resources beyond its specified limit. 50 00:05:08,470 --> 00:05:16,080 In case of the CPU, kubernetes throttles the CPU so that it does not go beyond the specified limit. 51 00:05:16,420 --> 00:05:20,910 A container cannot use more CPU resources than its limit. 52 00:05:20,950 --> 00:05:28,720 However, this is not the case with memory. A container CAN use more memory resources that its limit. 53 00:05:28,720 --> 00:05:35,800 So if a pod tries to consume more memory than its limit constantly, the POD will be terminated. 54 00:05:35,890 --> 00:05:39,340 Well that's it for this lecture on resource requirements in kubernetes. 55 00:05:39,340 --> 00:05:45,880 Head over to the coding exercises section and practice viewing configuring and troubleshooting 56 00:05:46,300 --> 00:05:49,310 resource requirements in kubernetes. 57 00:05:49,330 --> 00:05:51,520 Thank you and I will see you in the next lecture.