尝试输出Terraform的日志
首先
我打算试一下在terraform中，可以通过指定TRACE、DEBUG、INFO、WARN、ERROR等级来输出执行时的日志。试试看哪个级别会输出什么样的日志内容。
工作方法
我打算应用一个只包含创建ec2的简单tf文件，然后查看日志。
resource "aws_instance" "example" {
ami = "ami-0f9ae750e8274075b"
instance_type = "t2.micro"
}
以下是用于日志输出的命令。
TF_LOG=debug TF_LOG_PATH=/tmp/terraform_debug.log terraform apply
TF_LOG_PATH和TF_LOG用于指定输出日志级别和输出目标文件。本次选择了debug级别。
查看日志
应用后，文件被输出到通过TF_LOG_PATH指定的位置。
我立即想去查看，但是出现了大量的日志信息。
根据行数来看，
# cat /tmp/terraform_debug.log | wc -l
1767
创建了1767个EC2实例，但只是这样简单的操作却产生了大量的日志记录。
当使用头来稍微查看一下内容时，
# cat /tmp/terraform_debug.log | head
2021/03/18 09:40:53 [INFO] Terraform version: 0.12.24
2021/03/18 09:40:53 [INFO] Go runtime version: go1.12.13
2021/03/18 09:40:53 [INFO] CLI args: []string{"/usr/local/Cellar/tfenv/1.0.2/versions/0.12.24/terraform", "apply"}
2021/03/18 09:40:53 [DEBUG] Attempting to open CLI config file: /Users/******/.terraformrc
2021/03/18 09:40:53 [DEBUG] File doesn't exist, but doesn't need to. Ignoring.
2021/03/18 09:40:53 Loading CLI configuration from /Users/******/.terraform.d/credentials.tfrc.json
2021/03/18 09:40:53 [INFO] CLI command args: []string{"apply"}
2021/03/18 09:40:53 [WARN] Log levels other than TRACE are currently unreliable, and are supported only for backward compatibility.
Use TF_LOG=TRACE to see Terraform's internal logs.
----
除了DEBUG级别的日志之外，还有其他日志被输出。仔细想想，因为通常指定了以上级别的日志被输出，所以当然会出现这种情况。
那么，如果思考一下，是否没有输出关于 DEBUG 以下信息的 TRACE 呢？
# cat /tmp/terraform_debug.log | grep TRACE
2021/03/18 09:40:53 [WARN] Log levels other than TRACE are currently unreliable, and are supported only for backward compatibility.
Use TF_LOG=TRACE to see Terraform's internal logs.
2021/03/18 09:40:53 [WARN] Log levels other than TRACE are currently unreliable, and are supported only for backward compatibility.
Use TF_LOG=TRACE to see Terraform's internal logs.
2021-03-18T09:41:21.188+0900 [INFO] plugin.terraform-provider-aws_v3.29.0_x5: 2021/03/18 09:41:21 [TRACE] Waiting 3s before next try: timestamp=2021-03-18T09:41:21.187+0900
2021-03-18T09:41:24.469+0900 [INFO] plugin.terraform-provider-aws_v3.29.0_x5: 2021/03/18 09:41:24 [TRACE] Waiting 6s before next try: timestamp=2021-03-18T09:41:24.469+0900
2021-03-18T09:41:30.584+0900 [INFO] plugin.terraform-provider-aws_v3.29.0_x5: 2021/03/18 09:41:30 [TRACE] Waiting 10s before next try: timestamp=2021-03-18T09:41:30.584+0900
嗯嗯？有个[TRACE]呢。。从行头看起来，是不是先有[INFO]，所以这是[INFO]处理还是在执行命令时被忽略了，因为TF_LOG=debug和debug是小写指定的？
查看日志2
这次我们将销毁创建的环境，并尝试使用大写的TF_LOG=DEBUG进行指定。
TF_LOG=DEBUG TF_LOG_PATH=/tmp/terraform_debug2.log terraform apply
请再使用grep命令确认一次是否有TRACE输出。
# cat /tmp/terraform_debug2.log | grep TRACE 2021/03/18 10:05:38 [WARN] Log levels other than TRACE are currently unreliable, and are supported only for backward compatibility.
Use TF_LOG=TRACE to see Terraform's internal logs.
2021/03/18 10:05:38 [WARN] Log levels other than TRACE are currently unreliable, and are supported only for backward compatibility.
Use TF_LOG=TRACE to see Terraform's internal logs.
2021-03-18T10:06:07.952+0900 [INFO] plugin.terraform-provider-aws_v3.29.0_x5: 2021/03/18 10:06:07 [TRACE] Waiting 3s before next try: timestamp=2021-03-18T10:06:07.952+0900
2021-03-18T10:06:11.084+0900 [INFO] plugin.terraform-provider-aws_v3.29.0_x5: 2021/03/18 10:06:11 [TRACE] Waiting 6s before next try: timestamp=2021-03-18T10:06:11.084+0900
2021-03-18T10:06:17.511+0900 [INFO] plugin.terraform-provider-aws_v3.29.0_x5: 2021/03/18 10:06:17 [TRACE] Waiting 10s before next try: timestamp=2021-03-18T10:06:17.511+0900
你看起来很懂。那么，这似乎是被归类到了[INFO]。
查看日志3
我已经尝试过实际指定TRACE级别会发生什么情况了。
TF_LOG=TRACE TF_LOG_PATH=/tmp/terraform_trace.log terraform apply
我会确认TRACE的内容。
# cat /tmp/terraform_trace.log | grep TRACE | head
2021/03/18 10:11:00 [TRACE] Meta.Backend: built configuration for "s3" backend with hash value 873148124
2021/03/18 10:11:00 [TRACE] Preserving existing state lineage "c6ae9e85-4f2d-0e02-65e1-c6a98f94be5e"
2021/03/18 10:11:00 [TRACE] Preserving existing state lineage "c6ae9e85-4f2d-0e02-65e1-c6a98f94be5e"
2021/03/18 10:11:00 [TRACE] Meta.Backend: working directory was previously initialized for "s3" backend
2021/03/18 10:11:00 [TRACE] Meta.Backend: using already-initialized, unchanged "s3" backend configuration
2021/03/18 10:11:03 [TRACE] Meta.Backend: instantiated backend of type *s3.Backend
2021/03/18 10:11:03 [TRACE] Meta.Backend: backend *s3.Backend does not support operations, so wrapping it in a local backend
2021/03/18 10:11:03 [TRACE] backend/local: requesting state manager for workspace "default"
2021/03/18 10:11:03 [TRACE] backend/local: requesting state lock for workspace "default"
2021/03/18 10:11:03 [TRACE] backend/local: reading remote state for workspace "default"
刚才输出了大量的日志。当指定[TRACE]和[TRACE]级别的日志出现在[INFO]内时，它们似乎是不同类型的。
日志文件的内容被输出
由于数量庞大，无法详细查看，但内容中也包含了实例ID和IP地址等详细信息。如果从输出的日志中提取各种信息，自动化的工作将会变得更加顺利。
{
"version": 4,
"terraform_version": "0.12.24",
"serial": 2,
"lineage": "79a10223-15ac-3d6e-a5ad-ca554873829d",
"outputs": {},
"resources": [
{
"mode": "managed",
"type": "aws_instance",
"name": "example",
"provider": "provider.aws",
"instances": [
{
"schema_version": 1,
"attributes": {
"ami": "ami-0f9ae750e8274075b",
<省略>
