Metadata filtering with the meta primary

Note: Make sure you’ve set up the test environment so you can follow along in the tutorial.

This tutorial gives a detailed overview of the meta primary. The meta primary lets you filter entries on their metadata properties, which is useful when you want to filter entries on a non-Wash attribute property. Examples of such properties include vendor-specific things like an AWS EC2 instance’s VPC ID or a GCP compute instance’s service accounts. They also include properties that don’t yet exist as Wash attributes, such as a VM or container’s state, labels, and tags.

The meta primary is its own mini-DSL (domain specific language). Each meta primary expression consists of:

There are seven possible value types (excluding Primitive):

Each value type comes with its own predicate. For example, you would construct an Object Predicate on Object values, an Array Predicate on Array values, a Numeric Predicate on Numeric values, or a Time Predicate on Time values. All predicates evaluate to false for mistyped values. For example, an Object Predicate would return false for a Numeric value.

Each value predicate can be combined with another value predicate using find’s expression operators. For example, the predicate +1 is a numeric predicate that means > 1. The predicate +1 -a -3 means > 1 AND < 3. Similarly, the predicate +1 -o -3 means > 1 OR < 3.

To facilitate the following discussion, we will pretend that we are filtering on Docker containers. We will use the wash_tutorial_redis_1 container’s metadata when constructing our meta primary expressions.

wash . ❯ meta docker/containers/wash_tutorial_redis_1
AppArmorProfile: ""
- redis-server
- --appendonly
- "yes"
  AttachStderr: false
  AttachStdin: false
  AttachStdout: false
  - redis-server
  - --appendonly
  - "yes"
  Domainname: ""
  - PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
  - REDIS_DOWNLOAD_SHA=6624841267e142c5d5d5be292d705f8fb6070677687c5aad1645421a936d22b3
    6379/tcp: {}
  Hostname: 3b197bd973c6
  Image: redis:buster
    com.docker.compose.config-hash: 8c4cc3f3d32489df4e753d5e5fba27ad5f5c139b3858a4df71ef50c0b09b9238
    com.docker.compose.container-number: "1"
    com.docker.compose.oneoff: "False"
    com.docker.compose.project: wash_tutorial
    com.docker.compose.service: redis
    com.docker.compose.version: 1.24.1
  OnBuild: null
  OpenStdin: false
  StdinOnce: false
  Tty: false
  User: ""
    /data: {}
  WorkingDir: /data
Created: "2019-10-05T18:21:22.7854646Z"
Driver: overlay2
ExecIDs: null
    LowerDir: /var/lib/docker/overlay2/3982b2fb7f2cfdb74a8ca2344aeee684e1004cd4808c6205de6ff226715e49a9-init/diff:/var/lib/docker/overlay2/8af9dbb0afa2b0eac0b19360f3648d81821905ec2811215d5b4c1a15b5d46585/diff:/var/lib/docker/overlay2/1720b61f5dc9d53bf70613505efe82f7c96a27643688f780d1ded3c9e5ec7662/diff:/var/lib/docker/overlay2/bb1c27bd09c6a39423c065d957733f134f20bfafcbd8d136f796b3c2530b5f49/diff:/var/lib/docker/overlay2/3a1f448d51cbdbc4e6f4b8ff4f7e2b924dd01b382baf72e5987761bc1b570004/diff:/var/lib/docker/overlay2/777dacd8e37b2aa423f4bf565b60b06497d877c2a3cf182746dfae3387341255/diff:/var/lib/docker/overlay2/2b11fabdfd83518a5d386c38da90033e4035ab2969c8fa931f2ecc50d15c05c4/diff
    MergedDir: /var/lib/docker/overlay2/3982b2fb7f2cfdb74a8ca2344aeee684e1004cd4808c6205de6ff226715e49a9/merged
    UpperDir: /var/lib/docker/overlay2/3982b2fb7f2cfdb74a8ca2344aeee684e1004cd4808c6205de6ff226715e49a9/diff
    WorkDir: /var/lib/docker/overlay2/3982b2fb7f2cfdb74a8ca2344aeee684e1004cd4808c6205de6ff226715e49a9/work
  Name: overlay2
  AutoRemove: false
  - wash_tutorial_redis:/data:rw
  BlkioDeviceReadBps: null
  BlkioDeviceReadIOps: null
  BlkioDeviceWriteBps: null
  BlkioDeviceWriteIOps: null
  BlkioWeight: 0
  BlkioWeightDevice: null
  CapAdd: null
  CapDrop: null
  Capabilities: null
  Cgroup: ""
  CgroupParent: ""
  - 0
  - 0
  ContainerIDFile: ""
  CpuCount: 0
  CpuPercent: 0
  CpuPeriod: 0
  CpuQuota: 0
  CpuRealtimePeriod: 0
  CpuRealtimeRuntime: 0
  CpuShares: 0
  CpusetCpus: ""
  CpusetMems: ""
  DeviceCgroupRules: null
  DeviceRequests: null
  Devices: null
  Dns: null
  DnsOptions: null
  DnsSearch: null
  ExtraHosts: null
  GroupAdd: null
  IOMaximumBandwidth: 0
  IOMaximumIOps: 0
  IpcMode: shareable
  Isolation: ""
  KernelMemory: 0
  KernelMemoryTCP: 0
  Links: null
    Config: {}
    Type: json-file
  - /proc/asound
  - /proc/acpi
  - /proc/kcore
  - /proc/keys
  - /proc/latency_stats
  - /proc/timer_list
  - /proc/timer_stats
  - /proc/sched_debug
  - /proc/scsi
  - /sys/firmware
  Memory: 0
  MemoryReservation: 0
  MemorySwap: 0
  MemorySwappiness: null
  NanoCpus: 0
  NetworkMode: wash_tutorial_default
  OomKillDisable: false
  OomScoreAdj: 0
  PidMode: ""
  PidsLimit: null
    - HostIp: ""
      HostPort: "6379"
  Privileged: false
  PublishAllPorts: false
  - /proc/bus
  - /proc/fs
  - /proc/irq
  - /proc/sys
  - /proc/sysrq-trigger
  ReadonlyRootfs: false
    MaximumRetryCount: 0
    Name: ""
  Runtime: runc
  SecurityOpt: null
  ShmSize: 67108864
  UTSMode: ""
  Ulimits: null
  UsernsMode: ""
  VolumeDriver: ""
  VolumesFrom: []
HostnamePath: /var/lib/docker/containers/3b197bd973c6f4727f6b029ac52bf3332d964613de07913937583042ea06f153/hostname
HostsPath: /var/lib/docker/containers/3b197bd973c6f4727f6b029ac52bf3332d964613de07913937583042ea06f153/hosts
Id: 3b197bd973c6f4727f6b029ac52bf3332d964613de07913937583042ea06f153
Image: sha256:01a52b3b5cd14dffaff0908e242d11275a682cc8fe3906a0a7ec6f36fbe001f5
LogPath: /var/lib/docker/containers/3b197bd973c6f4727f6b029ac52bf3332d964613de07913937583042ea06f153/3b197bd973c6f4727f6b029ac52bf3332d964613de07913937583042ea06f153-json.log
MountLabel: ""
- Destination: /data
  Driver: local
  Mode: rw
  Name: wash_tutorial_redis
  Propagation: ""
  RW: true
  Source: /var/lib/docker/volumes/wash_tutorial_redis/_data
  Type: volume
Name: /wash_tutorial_redis_1
  Bridge: ""
  EndpointID: ""
  Gateway: ""
  GlobalIPv6Address: ""
  GlobalIPv6PrefixLen: 0
  HairpinMode: false
  IPAddress: ""
  IPPrefixLen: 0
  IPv6Gateway: ""
  LinkLocalIPv6Address: ""
  LinkLocalIPv6PrefixLen: 0
  MacAddress: ""
      - redis
      - 3b197bd973c6
      DriverOpts: null
      EndpointID: 3237602c94fb0f9838acb0cde2ff19e977c71bab16eec8ba18c1ddefb8405ad1
      GlobalIPv6Address: ""
      GlobalIPv6PrefixLen: 0
      IPAMConfig: null
      IPPrefixLen: 16
      IPv6Gateway: ""
      Links: null
      MacAddress: 02:42:ac:19:00:03
      NetworkID: f3d6e842b399a3edbd3eab9f37fdf767dd8071e4fff87cea93046d4d3d1c4712
    - HostIp:
      HostPort: "6379"
  SandboxID: 39a02f1301effce20d2e478bece77b6be47d8c27c9b69d4e430986c89317d4af
  SandboxKey: /var/run/docker/netns/39a02f1301ef
  SecondaryIPAddresses: null
  SecondaryIPv6Addresses: null
Platform: linux
ProcessLabel: ""
ResolvConfPath: /var/lib/docker/containers/3b197bd973c6f4727f6b029ac52bf3332d964613de07913937583042ea06f153/resolv.conf
RestartCount: 0
SizeRootFs: 98193890
SizeRw: 0
  Dead: false
  Error: ""
  ExitCode: 0
  FinishedAt: "0001-01-01T00:00:00Z"
  OOMKilled: false
  Paused: false
  Pid: 24408
  Restarting: false
  Running: true
  StartedAt: "2019-10-05T18:21:23.8614197Z"
  Status: running

Note: We’re using the full metadata because a Docker container’s partial metadata doesn’t have enough interesting properties for a meaningful tutorial. In general, you’d always want to use the partial metadata’s value instead of the full metadata because filtering on the former is much faster: O(1) vs. O(N), where N is the number of visited entries.

Now say we wanted to filter on a Docker container’s platform. From the meta output, we see that Platform is the desired property, and the value of that property is a String. The latter means that we will be using a String Predicate. Thus, the meta primary expression would look something like

-meta '.platform' linux

Let’s try it out!

wash . ❯ find docker -fullmeta -k '*container' -meta '.platform' linux

Note: The fullmeta option tells find that we are filtering on the entry’s full metadata.

Nice! Note that we used the kind primary to explicitly indicate that we are filtering on Docker containers. Also note that the meta primary will case property names for you, so you don’t have to be too strict when you’re typing them out. This means that something like -meta '.PLATFORM' linux or -meta '.pLaTfOrM' linux also work.

Now say we wanted to filter on all of our Docker containers whose maximum retry count is less than 1. From the meta output, we see that hostConfig.restartPolicy.maximumRetryCount is the desired property, and that this property is a numeric value. Thus, the expression would look something like

-meta '.hostConfig.restartPolicy.maximumRetryCount' -1

where -1 means < 1 (see the section on Numeric Predicates in the meta primary docs).

Let’s try it out!

wash . ❯ find docker -fullmeta -k '*container' -meta '.hostConfig.restartPolicy.maximumRetryCount' -1


Now say we wanted to filter on all of our Docker containers that have a mount named wash_tutorial_redis. From the meta output, we see that this information is contained in the mounts property. That property’s value is an array of mounts, and each mount is an object. For a given mount, it looks like the name would contain the mount’s name. From this information, we see that Return true if the Docker container has a mount named wash_tutorial_redis is equivalent to Return true if the Docker container’s mounts property contains at least one element whose name property is wash_tutorial_redis.

Now that we’ve more precisely defined our predicate, it is time to construct the meta primary expression. Since mounts is our property, we’ll start with -meta '.mounts'. Since mounts has an Array value, that means we must use an Array Predicate. Since our Array Predicate must return true if at least one element matches the final predicate, we’ll use [?]. Thus, our expression now becomes -meta '.mounts' '[?]'.

Each element in the array is an Object. That means we must give our Array Predicate an Object Predicate. Since the name property contains the desired information, our expression becomes -meta 'mounts' '[?]' '.name'. Since the name property is a String value, we must give our Object Predicate a String Predicate. We want to match on wash_tutorial_redis, so our expression now turns into

-meta '.mounts' '[?]' '.name' wash_tutorial_redis

and we are done. We can shorten this expression to

-meta '.mounts[?]' '.name' wash_tutorial_redis

or even further to

-meta '.mounts[?].name' wash_tutorial_redis

So the find invocation is something like:

find docker -fullmeta -k '*container' -meta '.mounts[?].name' wash_tutorial_redis

Try it out and see if it works.

That wraps up our discussion on the meta primary’s DSL. We’ll now give you a general overview of how to construct a meta primary expression. Assuming you have a general idea of the specific property that you want to filter on, then here’s what you should do:

  1. Find a representative entry that you can use to construct your expression. Our examples filtered Docker containers so they chose the wash_tutorial_redis container as the representative entry.

  2. Check that entry’s partial metadata value via meta --partial and see if the desired property is there. If it is, then figure out the property value’s type and construct the appropriate predicate. Remember that you can use find --help meta to view the meta primary’s full documentation.

  3. If the partial metadata does not contain the desired property, then you’ll have to check the entry’s full metadata via meta. If the full metadata contains the property, then refer to Step 2 and be sure to pass the -fullmeta option to find’s invocation so that find knows that it’ll need to fetch the entry’s full metadata. If the full metadata does not contain the property, then you’ll have to contact the plugin author(s) and ask them if they could include your property’s value in the entry’s metadata.

Note: The meta primary should be used in conjunction with the kind primary so that

Type find --help kind to see the kind primary’s documentation. The meta primary’s documentation also contains some good examples of the kind primary in action.


Some of these exercises will ask you questions about the other plugins. Please feel free to skip those exercises if you are unable to answer them.

  1. This exercise is broken up into several parts. Each part will ask you to filter on something specific to a Docker container. Your job is to provide the appropriate meta primary expression that accomplishes the given task. For example, a valid answer for “Has N < 1 maximum retry counts” would be -meta '.hostConfig.restartPolicy.maximumRetryCount' -1. Hint: Use the example’s metadata. Remember to set the fullmeta option when testing your expressions.

    1. Has N == 0 AND N < 1 maximum retry counts.

      Answer-meta '.hostConfig.restartPolicy.maximumRetryCount' 0 -a -1

    2. Has a mount whose name is either wash_tutorial_redis or wash_tutorial_web

      Answer-meta '.mounts[?]' '.name' wash_tutorial_redis -o wash_tutorial_web

    3. Was started within the last 4 weeks.

      Answer-meta '.state.startedAt' -4w

    4. Is not in the stopped state.

      Answer-meta '.state.status' \! stopped

    5. Has the wash_tutorial_redis volume mounted. Hint: The predicate is still constructed on the mounts property. What’s the property that corresponds to a mount’s type?

      Answer-meta '.mounts[?]' '.name' wash_tutorial_redis -a '.type' volume

  2. This exercise is broken up into several parts. Each part will ask you to find entries that satisfy a specific set of criteria. Your job is to provide the appropriate find invocation that accomplishes the given task. For example, a valid answer for “Find all EC2 instances with the project tag in a given profile” would be find aws/<profile> -k '*ec2*instance' -meta '.tags[?]' '.key' project. Hint: The partial metadata should contain what you need.

    Note: Even if you’re not using a given plugin, we recommend that you take a look at these answers to see the full extent of the meta primary’s power.

    1. Find all running Docker containers.

      Answerfind docker -k '*container' -meta '.state' running

    2. Find all running GCP compute instances in a given project.

      Answerfind gcp/<project> -k '*compute*instance' -meta '.status' RUNNING

    3. Find all running Kubernetes pods in a given context.

      Answerfind kubernetes/<context> -k '*pod' -meta '.status.phase' Running

    4. Find all GCP storage buckets in a given project that are using REGIONAL storage.

      Answerfind gcp/<project> -k '*storage*bucket' -meta '.storageClass' REGIONAL. Remember that the concepts in this tutorial apply to any entry, not just containers/VMs

    5. Find all running Docker containers that were created within the last 24 hours. Hint: Remember the crtime primary and find’s operators.

      Answerfind docker -k '*container' -meta '.state' running -crtime -24h

    6. Find all running AWS EC2 instances in a given profile that were launched more than a week ago. Hint: You’ll need to use the meta primary more than once here.

      Answerfind aws/<profile> -k '*ec2*instance' -meta '' running -meta '.launchTime' +1w

    7. Find all running GCP compute instances in a given project whose owner label is set to jimmy.

      Answerfind gcp/<project> -k '*compute*instance' -meta '.status' RUNNING -meta '.labels.owner' jimmy

    8. Find all Kubernetes pods in a given context that have the owner label. Hint: It is enough to check that the label exists.

      Answerfind kubernetes/<context> -k '*pod' -meta '.metadata.labels.owner' -exists

Next steps

That’s the end of the Filtering entries with find series! Click here to go back to the tutorials page.