github.com/lalkh/containerd@v1.4.3/docs/ops.md (about)

     1  # containerd for Ops and Admins
     2  
     3  containerd is meant to be a simple daemon to run on any system.
     4  It provides a minimal config with knobs to configure the daemon and what plugins are used when necessary.
     5  
     6  ```
     7  NAME:
     8     containerd -
     9                      __        _                     __
    10    _________  ____  / /_____ _(_)___  ___  _________/ /
    11   / ___/ __ \/ __ \/ __/ __ `/ / __ \/ _ \/ ___/ __  /
    12  / /__/ /_/ / / / / /_/ /_/ / / / / /  __/ /  / /_/ /
    13  \___/\____/_/ /_/\__/\__,_/_/_/ /_/\___/_/   \__,_/
    14  
    15  high performance container runtime
    16  
    17  
    18  USAGE:
    19     containerd [global options] command [command options] [arguments...]
    20  
    21  VERSION:
    22     v1.0.0-alpha3-36-ge9b86af
    23  
    24  COMMANDS:
    25       config   information on the containerd config
    26       help, h  Shows a list of commands or help for one command
    27  
    28  GLOBAL OPTIONS:
    29     --config value, -c value     path to the configuration file (default: "/etc/containerd/config.toml")
    30     --log-level value, -l value  set the logging level [debug, info, warn, error, fatal, panic]
    31     --address value, -a value    address for containerd's GRPC server
    32     --root value                 containerd root directory
    33     --help, -h                   show help
    34     --version, -v                print the version
    35  ```
    36  
    37  While a few daemon level options can be set from CLI flags the majority of containerd's configuration is kept in the configuration file.
    38  The default path for the config file is located at `/etc/containerd/config.toml`.
    39  You can change this path via the `--config,-c` flags when booting the daemon.
    40  
    41  ## systemd
    42  
    43  If you are using systemd as your init system, which most modern linux OSs are, the service file requires a few modifications.
    44  
    45  ```systemd
    46  [Unit]
    47  Description=containerd container runtime
    48  Documentation=https://containerd.io
    49  After=network.target
    50  
    51  [Service]
    52  ExecStartPre=-/sbin/modprobe overlay
    53  ExecStart=/usr/local/bin/containerd
    54  Delegate=yes
    55  KillMode=process
    56  
    57  [Install]
    58  WantedBy=multi-user.target
    59  ```
    60  
    61  `Delegate=yes` and `KillMode=process` are the two most important changes you need to make in the `[Service]` section.
    62  
    63  `Delegate` allows containerd and its runtimes to manage the cgroups of the containers that it creates.
    64  Without setting this option, systemd will try to move the processes into its own cgroups, causing problems for containerd and its runtimes to properly account for resource usage with the containers.
    65  
    66  `KillMode` handles when containerd is being shut down.
    67  By default, systemd will look in its named cgroup and kill every process that it knows about for the service.
    68  This is not what we want.
    69  As ops, we want to be able to upgrade containerd and allow existing containers to keep running without interruption.
    70  Setting `KillMode` to `process` ensures that systemd only kills the containerd daemon and not any child processes such as the shims and containers.
    71  
    72  The following `systemd-run` command starts containerd in a similar way:
    73  ```
    74  sudo systemd-run -p Delegate=yes -p KillMode=process /usr/local/bin/containerd
    75  ```
    76  
    77  ## Base Configuration
    78  
    79  In the containerd config file you will find settings for persistent and runtime storage locations as well as grpc, debug, and metrics addresses for the various APIs.
    80  
    81  There are a few settings that are important for ops.
    82  The first setting is the `oom_score`.  Because containerd will be managing multiple containers, we need to ensure that containers are killed before the containerd daemon in an out of memory condition.
    83  We also do not want to make containerd unkillable, but we want to lower its score to the level of other system daemons.
    84  
    85  containerd also exports its own metrics as well as container level metrics via the prometheus metrics format.
    86  Currently, prometheus only supports TCP endpoints, therefore, the metrics address should be a TCP address that your prometheus infrastructure can scrape metrics from.
    87  
    88  containerd also has two different storage locations on a host system.
    89  One is for persistent data and the other is for runtime state.
    90  
    91  `root` will be used to store any type of persistent data for containerd.
    92  Snapshots, content, metadata for containers and image, as well as any plugin data will be kept in this location.
    93  The root is also namespaced for plugins that containerd loads.
    94  Each plugin will have its own directory where it stores data.
    95  containerd itself does not actually have any persistent data that it needs to store, its functionality comes from the plugins that are loaded.
    96  
    97  
    98  ```
    99  /var/lib/containerd/
   100  ├── io.containerd.content.v1.content
   101  │   ├── blobs
   102  │   └── ingest
   103  ├── io.containerd.metadata.v1.bolt
   104  │   └── meta.db
   105  ├── io.containerd.runtime.v1.linux
   106  │   ├── default
   107  │   └── example
   108  ├── io.containerd.snapshotter.v1.btrfs
   109  └── io.containerd.snapshotter.v1.overlayfs
   110      ├── metadata.db
   111      └── snapshots
   112  ```
   113  
   114  `state` will be used to store any type of ephemeral data.
   115  Sockets, pids, runtime state, mount points, and other plugin data that must not persist between reboots are stored in this location.
   116  
   117  ```
   118  /run/containerd
   119  ├── containerd.sock
   120  ├── debug.sock
   121  ├── io.containerd.runtime.v1.linux
   122  │   └── default
   123  │       └── redis
   124  │           ├── config.json
   125  │           ├── init.pid
   126  │           ├── log.json
   127  │           └── rootfs
   128  │               ├── bin
   129  │               ├── data
   130  │               ├── dev
   131  │               ├── etc
   132  │               ├── home
   133  │               ├── lib
   134  │               ├── media
   135  │               ├── mnt
   136  │               ├── proc
   137  │               ├── root
   138  │               ├── run
   139  │               ├── sbin
   140  │               ├── srv
   141  │               ├── sys
   142  │               ├── tmp
   143  │               ├── usr
   144  │               └── var
   145  └── runc
   146      └── default
   147          └── redis
   148              └── state.json
   149  ```
   150  
   151  Both the `root` and `state` directories are namespaced for plugins.
   152  Both directories are an implementation detail of containerd and its plugins.
   153  They should not be tampered with as corruption and bugs can and will happen.
   154  External apps reading or watching changes in these directories have been known to cause `EBUSY` and stale file handles when containerd and/or its plugins try to cleanup resources.
   155  
   156  ```toml
   157  # persistent data location
   158  root = "/var/lib/containerd"
   159  # runtime state information
   160  state = "/run/containerd"
   161  # set containerd's OOM score
   162  oom_score = -999
   163  
   164  # grpc configuration
   165  [grpc]
   166    address = "/run/containerd/containerd.sock"
   167    # socket uid
   168    uid = 0
   169    # socket gid
   170    gid = 0
   171  
   172  # debug configuration
   173  [debug]
   174    address = "/run/containerd/debug.sock"
   175    # socket uid
   176    uid = 0
   177    # socket gid
   178    gid = 0
   179    # debug level
   180    level = "info"
   181  
   182  # metrics configuration
   183  [metrics]
   184    # tcp address!
   185    address = "127.0.0.1:1234"
   186  ```
   187  
   188  ## Plugin Configuration
   189  
   190  At the end of the day, containerd's core is very small.
   191  The real functionality comes from plugins.
   192  Everything from snapshotters, runtimes, and content are all plugins that are registered at runtime.
   193  Because these various plugins are so different we need a way to provide type safe configuration to the plugins.
   194  The only way we can do this is via the config file and not CLI flags.
   195  
   196  In the config file you can specify plugin level options for the set of plugins that you use via the `[plugins.<name>]` sections.
   197  You will have to read the plugin specific docs to find the options that your plugin accepts.
   198  
   199  ### Linux Runtime Plugin
   200  
   201  The linux runtime allows a few options to be set to configure the shim and the runtime that you are using.
   202  
   203  ```toml
   204  [plugins.linux]
   205  	# shim binary name/path
   206  	shim = ""
   207  	# runtime binary name/path
   208  	runtime = "runc"
   209  	# do not use a shim when starting containers, saves on memory but
   210  	# live restore is not supported
   211  	no_shim = false
   212  	# display shim logs in the containerd daemon's log output
   213  	shim_debug = true
   214  ```
   215  
   216  ### Bolt Metadata Plugin
   217  
   218  The bolt metadata plugin allows configuration of the content sharing policy between namespaces.
   219  
   220  The default mode "shared" will make blobs available in all namespaces once it is pulled into any namespace.
   221  The blob will be pulled into the namespace if a writer is opened with the "Expected" digest that is already present in the backend.
   222  
   223  The alternative mode, "isolated" requires that clients prove they have access to the content by providing all of the content to the ingest before the blob is added to the namespace.
   224  
   225  Both modes share backing data, while "shared" will reduce total bandwidth across namespaces, at the cost of allowing access to any blob just by knowing its digest.
   226  
   227  The default is "shared". While this is largely the most desired policy, one can change to "isolated" mode with the following configuration:
   228  
   229  ```toml
   230  [plugins.bolt]
   231  	content_sharing_policy = "isolated"
   232  ```